Temperature differences and calculations

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Exercise 1.1
1. Following the number line shows the temperature in (°C) on different places
on a particular day.
Answer:
(a) Observe this number line and write the temperature on it.
Answer: By observing this number line we understand that
Temperature at Lahulspiti = (-8) °C
Temperature at Srinagar = (-2) °C
Temperature at Shimla = 5 °C
Temperature at Ooty = 14°C
Temperature at Bengaluru = 22°C
(b) Write the temperature difference between the hottest and the coldest places
among the above
Hottest place = Bengaluru (22°C)
Coldest Place = Lahulspiti (-8) °C
Therefore, 22 – (-8)
= 22°C + 8
= 30°C
Hence, the temperature difference between the hottest and the coldest place above is
(30°C)
(c) What is the temperature difference between Lahulspiti and Srinagar?
Answer:
Temperature at Lahulspiti = (-8) °C
Temperature at Srinagar = (-2) °C
Temperature difference between Lahulspiti and Srinagar = (-8) °C - (-2) °C
= (-8) °C + 2°C = (-6) °C
Hence, the temperature difference between Lahulspiti and Srinagar is (-6) °C.
(d) Can we say temperature of Srinagar and Shimla taken together is less than
the temperature at Shimla? Is it also less than the temperature at Srinagar?
Answer:
The temperature at Srinagar = 5 °C
The temperature at Shimla = (-2) °C
Total Temperature at Srinagar and Shimla = 5 °C + (-2) °C = 3°C
5°C > 3°C

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Therefore, temperature of Srinagar and Shimla taken together is less than the
temperature at Srinagar.
Now,
(-2) °C < 3°C
Therefore, temperature of Srinagar and Shimla taken together is not less than the
temperature at Shimla.
2. In a quiz, positive marks are given for correct answers and negative marks are
given for incorrect answers. If Jack’s scores in five successive rounds were 25,
– 5, – 10, 15 and 10, what was his total at the end?
Answer:
Marks Jack scored in 5 successive rounds = 25, – 5, – 10, 15 and 10
Total score of Jack in that test = 25, – 5, – 10, 15 and 10
= 25, – 5, – 10, 15 and 10
= 35
Hence, Jack scored 35 marks in 5 successive rounds of the test.
3. At Srinagar temperature was – 5°C on Monday and then it dropped by 2°C on
Tuesday. What was the temperature of Srinagar on Tuesday? On Wednesday, it
rose by 4°C. What was the temperature on this day?
Answer:
Temperature on Monday at Srinagar = (– 5°C)
Temperature that felled on Tuesday = 2°C
Temperature that rose on Wednesday = 4°C
So, temperature at Tuesday will be = (- 5°C) - 2°C
= (- 7°C)
Now,
Temperature at Wednesday will be = (- 7°C) + 4°C
= (- 3°C)
Hence the temperature on Tuesday and Wednesday will be (- 7°C) and (- 3°C)
4. A plane is flying at the height of 5000 m above the sea level. At a particular
point, it is exactly above a submarine floating 1200 m below the sea level. What
is the vertical distance between them?

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Answer:
Height at which plane is flying (above the see level) = 5000m
Depth of the submarine from the sea level = 1200m
Vertical distance between them = 5000m - (- 1200) m
= 5000m - (- 1200) m
= 5000m + 1200m
= 6200m
∴ The vertical distance between the plane and the submarine is 6200m.
5. Mohan deposits ₹ 2,000 in his bank account and withdraws ₹ 1,642 from it, the
next day. If withdrawal of amount from the account is represented by a negative
integer, then how will you represent the amount deposited? Find the balance in
Mohan’s account after the withdrawal.
Answer:
We know,
Withdrawal from the account is represented by a negative integer.
Money deposited by Mohan = ₹2000
Money withdrew by Mohan next day = ₹ (- 1642)
Now,
Depositing of money is represented by a Positive integer.
Balance of Mohan’s bank account after the withdrawal of money on the next of
depositing money
= ₹2000 + (- 1642)
= ₹2000 - 1642
= ₹ 358
Hence, the depositing of money is represented by a positive integer and the balance
after the withdrawal of money from Mohan’s bank is ₹ 358

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6. Rita goes 20 km towards east from a point A to the point B. From B, she
moves 30 km towards west along the same road. If the distance towards east is
represented by a positive integer then, how will you represent the distance
travelled towards west? By which integer will you represent her final position
from A?
Answer:
We know that the distance towards East is represented by a Positive Integer.
So, the distance travelled towards west is represented by a Negative Integer.
Distance travelled by Rita in east direction = (20 Kilometer)
Distance travelled by Rita in west direction = (- 30 Kilometer)
Distance travelled to east to west
= 20 + (- 30)
= 20 - 30
= (- 10 Kilometer)
Hence, distance travelled towards west is represented by a negative integer. Rita
travels (- 10 Kilometer) towards west.
7. In a magic square each row, column and diagonal have the same sum. Check
which of the following is a magic square.
Answer:
(i) First we will find the sum of the rows
The sum along the first row = 5 + (- 1) + (- 4) = 0
The sum along the second row = (- 5) + (- 2) + 7 = 0
The sum along the third row = 0 + 3 + (- 3) = 0
Now we will find the sum of the columns,
The sum along the first column = 5 + (- 5) + 0 = 0
The sum along the second column = (- 1) + (- 2) + 3 = 0
The sum along the third column = (- 4) + (- 7) + 3 = 0

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Now, we will take out the sum of diagonals
The sum along the first diagonal = 5 + (- 2) + (- 3) = 0
The sum along the second diagonal = (- 4) + (- 2) + 0 = (- 6)
Hence, it’s not a magic square because one of its diagonal is (- 6) and the other all
columns, rows and diagonals have the sum 0.
(ii) First we will find the sums of the rows.
The sum along the first row = 1 + (- 10) + 0 = (- 9)
The sum along the second row = (- 4) + (- 3) + (- 2) = (- 9)
The sum along the third row = (- 6) + (- 4) + (- 2) = (- 9)
Now, we will consider the columns
The sum along the first column = 1 + (- 4) + (- 6) = (- 9)
The sum along the second column = (- 10) + (- 3) + 4 = (- 9)
The sum along the third column = 0 + (- 2) + (- 7) = (- 9)
Now, we will consider the diagonals
The sum along the first diagonal = 1 + (- 3) + (- 7) = (- 9)
The sum along the second diagonal = (- 6) + (- 3) + 0 = (- 9)
Hence (ii) is a magic square because the sum of all the rows, columns and diagonals is
same which is (- 9).
8. Verify a – (– b) = a + b for the following values of a and b.
(i) a = 21, b = 18
Answer:
a = 21 and b = 18
To verify this we will take out the L.H.S
= a - (- b)
= 21 - (- 18)
= 21 + 18
= 39
Hence, the value of L.H.S is 39
The R.H.S of this is
= a + b
= 21 + 18
= 39
The value of both L.H.S (Left hand side) and R.H.S (Right hand side) is same
= L.H.S = R.H.S

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39 = 39
Hence the value of a and b is satisfied.
(ii) a = 118, b = 125
To verify this we will take out the L.H.S
= a - (- b)
= 118 + (- 125)
= 118 + 125
= 243
The R.H.S of it is
= a + b
= 118 + 125
= 243
The value of both L.H.S and R.H.S is same
= L.H.S = R.H.S
243 = 243
Hence, the value of a and b is satisfied
(iii) a = 75, b = 84
To verify we will take out the L.H.S
= a - (- b)
= 75 - (- 84)
= 75 + 84
= 159
The R.H.S of it is
= a + b
= 75 + 84
= 159
= L.H.S = R.H.S
159 = 159
Hence, the value of a and b is satisfied.
(iv) a = 28, b = 11
To verify we will take out the L.H.S
= a - (- b)
= 28 - (- 11)
= 28 + 11

7
= 39
Now,
We will take out the R.H.S of the following.
= a + b
= 28 + 11
= 39
= L.H.S = R.H.S
39 = 39
Hence, the value of a and b is satisfied.
9. Use the sign of >, < or = in the box to make the statements true.
(a) (- 8) + (- 4) (- 8) - (- 4)
Answer:
To find the answer we will take out the L.H.S and the R.H.S
The L.H.S of the following is
= (- 8) + (- 4)
= (- 8) - 4
= (- 12)
The R.H.S of the following is
= (- 8) - (- 4)
= (- 8) + 4
= (- 4)
Therefore, (a) (- 8) + (- 4) < (- 8) - (- 4)
So, (- 8) + 4 > (- 8) - (- 4)
(b) (- 3) + 7 - (19) 15 - 8 + (- 9)
Answer:
To find the answer of the following we will find the L.H.S and the R.H.S of the following
= (- 3) + 7 - 19
= (- 15)
= 15 - 8 + (- 9)
= (- 2)
Therefore, (- 15) < (- 2)
So, (- 3) + 7 - 19 < 15 - 8 + (- 9)
(c) 23 - 41 + 11 23 - 41 -11
Answer:

8
= {23 - 41} + 11
= {23 - 41}
= (- 18)
= (- 18) + 11
= (- 7)
= 23 - 41 - 11
= {23 - 41}
= (- 18) - 11
= (- 29)
Therefore, (- 7) > (- 29)
So, 23 - 41 + 11 > 24 - 41 -11
(d) 39 + (- 24) - (15) 36 + (- 52) - (- 36)
Answer:
Answer:
= 39 + (- 24) - 15
= 39 - 24
= 15
= 15 - 15
= 0
= 36 + (- 52) - (- 36)
= 36 - 52 + 36
= 36 - 52
= (- 16) + 36
= 20
Therefore, 0 > 20
So, 39 + (- 24) - 15 < 36 + (- 52) - (- 36)
(e) - 231 + 79 + 51 - 399 + 159 + 81
Answer:
= - 231 + 79 + 51
= 79 + 51

9
= 130
= - 231 + 130
= - 101
Now,
= - 399 + 159 + 81
= 159 + 81
= 250
= - 399 + 250
= (- 149)
Therefore, (- 101) > (- 149)
So, - 231 + 79 + 51 > - 399 + 159 + 81
10. A water tank has steps inside it. A monkey is sitting on the topmost step (i.e.,
the first step). The water level is at the ninth step.
Answer:
(i) He jumps 3 steps down and then jumps back 2 steps up. In how many jumps
will he reach the water level?
Answer:
Let us consider steps moved down are represented by positive integers and then,
steps moved up are represented by negative integers.
As; initially the monkey was sitting at the first step.
In 1st
jump monkey will be at step = 1 + 3 = 4 steps
In 2nd
jump monkey will be at step = 4 + (-2) = 4 – 2 = 2 steps
In 3rd
In 4th
In 5th

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In 6th
In 7th
In 8th
In 9th
In 10th
In 11th
∴Monkey took 11 jumps or 9th
step to reach the water level.
(ii) After drinking water, he wants to go back. For this, he jumps 4 steps up and
then jumps back 2 steps down in every move. In how many jumps will he reach
back the top step?
Answer:
Let us consider steps moved down are represented by positive integers and then,
steps moved up are represented by negative integers.
Initially monkey is sitting on the ninth step i.e., at the water level
In 1st
In 2nd
In 3rd
In 4th
In 5th
jump monkey will be at step = 5 + (-4) = 5 – 4 = 1 step
∴Monkey took 5 jumps to reach back the top step i.e., first step.
(iii) If the number of steps moved down is represented by negative integers and
the number of steps moved up by positive integers, represent his moves in part
(i) and (ii) by completing the following; (a) – 3 + 2 – … = – 8 (b) 4 – 2 + … = 8. In
(a) the sum (– 8) represents going down by eight steps. So, what will the sum 8
in (b) represent?
Answer:
If the number of steps moved down is represented by negative integers and the
number of steps moved up by positive integers.
Monkey moves in part (i)
= – 3 + 2 – ……….. = – 8
Then LHS = – 3 + 2 – 3 + 2 – 3 + 2 – 3 + 2 – 3 + 2 – 3
= – 18 + 10
= – 8
RHS = -8
∴Moves in part (i) represents monkey is going down 8 steps. Because negative integer.
Now,

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Monkey moves in part (ii)
= 4 – 2 + ……….. = 8
Then LHS = 4 – 2 + 4 – 2 + 4
= 12 – 4
= 8
RHS = 8
∴Moves in part (ii) represents monkey is going up 8 steps. Because positive integer.
Exercise 1.2
1. Write down a pair of integers whose:
(a) Sum is -7
Answer:
(- 5) + (- 2)
= (- 5) - 2
= (- 7)
Therefore, there are many pairs of integers such as given above.
(b) difference is – 10
Answer:
(- 26) - (- 16)
= (- 26) + 16
= (- 10)
(c) sum is 0
(- 116) + 116
= (- 116) + 116
= 0
2.
(a) Write a pair of negative integers whose difference gives 8
Answer:
= (- 12) - (- 20)
= (- 12) + 20
= (- 12) + 12 = 0
= 20 - 12
= 8

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(b) Write a negative integer and a positive integer whose sum is – 5.
Answer:
= (- 32) + 27
= (- 5)
(c) Write a negative integer and a positive integer whose difference is – 3.
Answer:
= (- 6) - (- 3)
= (- 6) + 3
= (- 3)
3. In a quiz, team A scored – 40, 10, 0 and team B scored 10, 0, – 40 in three
successive rounds. Which team scored more? Can we say that we can add
integers in any order?
Answer:
From the question we know that
The score of Team A = (- 40), 10, 0
The total score obtained by team A is = (- 40) + 10 + 0
= (- 30)
The score of Team B in 3 successive rounds = 10, 0, (- 40)
The total score obtained by team B is = 10 + 0 + (- 40)
= (- 30)
Thus, the score of both Team A and Team B is same.
Therefore, we can say that we can add the integers in any order.
4. Fill in the blanks to make the following statements true:
(i) (–5) + (– 8) = (– 8) + (…………)
Answer:
Let’s name the missing integer (m)
(–5) + (– 8) = (– 8) + (…………)
(- 5) + (- 8)
= (- 5) - 8
= 13
By sending (- 8) from R.H.S to L.H.S it becomes 8
= (- 13) + 8
= (- 5)

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Therefore, the missing value (i.e. m) is (- 5)
Now substitute the value of x
(–5) + (– 8) = (– 8) + (- 5) …
[This equation is in the form of Commutative law of Addition]
(ii) –53 + ………… = –53
–53 + ………… = –53
It mean’s (- 53) + (m) = (- 53)
By sending (- 53) from R.H.S to L.H.S it becomes 53
So,
(- 53) + 53 = 0
Therefore, the missing value (i.e. m) is 0
(- 53 + 0 = (- 53)
[This equation is in the form of Closure property of Addition]
(iii) 17 + ………… = 0
17 + ………… = 0
It means 17 + m = 0
By sending 17 from R.H.S to L.H.S it becomes (- 17)
(m) = 0 - 17
x = (- 17)
17 + (-17) = 0 … [This equation is in the form of Closure property of Addition]
= 17 + (- 17) =
= 17 - 17 = 0
(iv) [13 + (– 12)] + (…………) = 13 + [(–12) + (–7)]
Answer:
[13 + (– 12)] + …….. = 13 + [(–12) + (–7)]
It means [13 + (– 12)] + (m) = 13 + [(–12) + (–7)]
= [13 - 12] + (m) = 13 + [- 12 - 7]
= 1 + (m) = 13 + (- 19)
= 1 + (m) = 13 - 19
= 1 + (m) = (- 6)
By sending 1 from LHS to RHS it becomes -1

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(m) = (- 6) + (- 1)
= (- 6) - 1
= (- 7)
= [13 + (– 12)] + (-7) = 13 + [(–12) + (–7)] …
[This equation is in the form of Associative property of Addition]
(v) (– 4) + [15 + (–3)] = [– 4 + 15] +…………
Answer:
(– 4) + [15 + (–3)] = [– 4 + 15] + ………..
= (– 4) + [15 – 3)] = [– 4 + 15] + (m)
= (-4) + [12] = [11] + (m)
= 8 = 11 + x
By sending 11 from RHS to LHS it becomes -11
= 8 – 11 = m
= (m) = -3
Therefore, the missing value (i.e. m) is
= (– 4) + [15 + (–3)] = [– 4 + 15] + -3 …
[This equation is in the form of Associative property of Addition]
Exercise 1.3 (Page Number - 21)
1. Find each of the following products:
(a) 3 × (–1)
Answer:
We’ll use the rule of Multiplication
= 3 x (- 1)
As there is only 1 negative integer the answer will also be in negative integer.
= 3 x (- 1)
= (- 3)
Therefore, (- 3) is the answer.
(b) (–1) × 225
Answer:
We’ll use the rule of Multiplication
= (- 1) x 225
As there is only 1 negative integer the answer will also be in negative integer.
= (- 1) x 225

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= (- 225)
(c) (–21) × (–30)
Answer:
We will use the rule of multiplication
= (– 21) × (– 30)
As there are two negative integers the answer will be in Positive integer.
= (– 21) × (– 30)
= 630
Therefore, 630 is the answer.
(d) (–316) × (–1)
Answer:
= (– 316) × (– 1)
= (– 316) × (– 1)
= 316
Therefore, the answer is 316
(e) (–15) × 0 × (–18)
Answer:
= (–15) × 0 × (–18)
= 0
Any integer multiplied by 0 the product is 0 only.
(f) (–12) × (–11) × (10)
Answer:
= (–12) × (–11) × (10)
= (–12) × (–11) × (10)
= (–12) × (–11)
= 132
= 132 × 10
= 1320

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(g) 9 × (–3) × (– 6)
Answer:
= 9 × (–3) × (– 6)
= (- 3) × (- 6)
= 18
= 9 × 18
= 162
(h) (–18) × (–5) × (– 4)
Answer:
As there are three negative integers the answer will be in negative integer
= (–18) × (–5) × (– 4)
= (- 18) × (- 5)
= 90
= 90 × (- 4)
= (- 360)
Therefore, the answer is (- 360)
(i) (–1) × (–2) × (–3) × 4
Answer:
As there are three negative integers the answer will be in negative integer
= (–1) × (–2) × (–3)
= (- 6)
= (- 6) × 4
= (- 24)
Therefore, the answer is (- 24)
(j) (–3) × (–6) × (–2) × (–1)
Answer:
As there are four negative integers the answer will be in positive integer.
= [(–3) × (–6)] × [(–2) × (–1)]
= [(–3) × (–6)]
= 18

17
= [(–2) × (–1)]
= 2
= 18 × 2
= 36
Therefore, the answer is 36.
2. Verify the following:
(a) 18 × [7 + (–3)] = [18 × 7] + [18 × (–3)]
Answer:
We will find out the L.H.S and the R.H.S of the following to verify the following.
The L.H.S of the following
First we’ll solve the question in the bracket
= 18 × [7 + (–3)]
= 18 × 7 - 3
= 18 × 4
= 72
Now,
= 18 × 7
= 126 + [18 × (–3)]
= [18 × (–3)]
= (- 54)
= 126 + (- 54)
= 126 - 54
72 = 72
Therefore, L.H.S = R.H.S
So, the equation is verified
(b) (–21) × [(– 4) + (– 6)] = [(–21) × (– 4)] + [(–21) × (– 6)]
Answer:
We will find out the L.H.S and the R.H.S of the following to verify the following.
The L.H.S of the following
= (–21) × [(– 4) + (– 6)]
= (–21) × [(- 4) - 6]
= (- 21) × (- 10)
= 210
So the L.H.S is 210
Now,

18
= [(–21) × (– 4)] + [(–21) × (– 6)]
= (- 21) × (- 4)
= 84
= (- 21) × (- 6)
= 126
= 126 + 84
= 210
210 = 210
Therefore L.H.S = R.H.S
So, the equation is verified.
3.
(i) For any integer a, what is (–1) × a equal to?
Answer:
= (-1) × a = -a
Therefore, when we multiplied any integer (a) with -1, then we get additive inverse of
that integer.
(ii) Determine the integer whose product with (–1) is
Answer:
(a) –22
Answer:
Now, multiply -22 with (-1), we get
= -22 × (-1)
= 22
Because, when we multiplied integer -22 with -1, then we get additive inverse of that
integer.
(b) 37
Answer:
Now, multiply 37 with (-1), we get
= 37 × (-1)
= -37
Because, when we multiplied integer 37 with -1, then we get additive inverse of that
integer.
(c) 0
Answer:
Now, multiply 0 with (-1), we get
= 0 × (-1)
= 0

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As, the product of zero give zero only.
4. Starting from (–1) × 5, write various products showing some pattern to show
(–1) × (–1) = 1.
Solution:-
The various products are,
= -1 × 5 = -5
= -1 × 4 = -4
= -1 × 3 = -3
= -1 × 2 = -2
= -1 × 1 = -1
= -1 × 0 = 0
= -1 × -1 = 1
We concluded that the product of one negative integer and one positive integer is
negative integer. Then, the product of two negative integers is a positive integer.
5. Find the product, using suitable properties:
(a) 26 × (– 48) + (– 48) × (–36)
Answer:
The given equation can be solved with the Distributive Law
Formulae of Distributive Law
= a × (b + c) = (a × b) + (a × c)
Let say a - 48, b - 26, c - (- 36)
Now,
= 26 × (– 48) + (– 48) × (–36)
= - 48 × (26 + (-36)
= 26 - 36
= (- 10)
= (- 48 × (- 10)
= 480
Therefore, 480 is the answer
(b) 8 × 53 × (–125)
Answer:
The given equation can be solved with the Commutative Law.
Formulae of Commutative Law
= a × b = b × a
Let a - 8, b - 53, c - (- 125)
Then,
= 8 × 53 × (–125)
= 8 × (- 125)

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= (- 1000)
= (- 1000) × 53
= (- 53000)
(c) 15 × (–25) × (– 4) × (–10)
Answer:
We will solve this question with commutative law of Multiplication
Formulae of Commutative Law
= a × b = b × a
Then,
= 15 × [(- 25) × (- 4)]
= 15 × 100
= 1500
= 1500 × (- 10)
= (- 15000)
(d) (– 41) × 102
Answer:
We will solve this question with Distributive Law of Multiplication.
= a × (b + c) = a × b + a × c
Then,
= (- 41) × 102
= (- 41) × (100 + 2)
= (- 41 × 100) + (- 41 × 2)
= (- 41 × 100)
= (- 4100) + (- 41× 2)
= (- 41) × 2
= (- 82)
= (- 4100) + (- 82)
= (- 4100) - 82
= (- 4,182)
Therefore, (- 4,182) is the answer.
(e) 625 × (–35) + (– 625) × 65
Answer:

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= a × (b + c) = a × b + a × c
Then,
= 625 × (- 35) + (- 65)
= (- 35) + (- 65)
= (- 100)
= 625 × (- 100)
= (- 62,500)
(f) 7 × (50 – 2)
Answer:
= a × (b + c) = a × b + a × c
Then,
= 7 × 50 - 7 × 2
= 7 × 50
= 350
= 7 × 2
= 14
= 350 - 14
= 336
(g) (–17) × (–29)
Answer:
= a × (b + c) = a × b + a × c
Then,
= (- 17) × (- 29)
= (- 17) × (30 + 1)
= (- 17) × 30
= (510)
= (-17 × 1)
= (- 17)
= (510 + (- 17)
= (510 - 17)
= (493)

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(h) (–57) × (–19) + 57
Answer:
= a × (b + c) = a × b + a × c
Then,
= (- 57) × (- 19) + (- 57) × 1
Simplifying
= (- 57) × [(- 19 + 1)
= (- 57) × (- 20)
= 1140
6. A certain freezing process requires that room temperature be lowered from
40°C at the rate of 5°C every hour. What will be the room temperature 10 hours
after the process begins?
Answer:
From the question we know that,
Temperature of the room before the process started = 40°C
Rate of temperature being lowered down = 5°C per hour
Room Temperature after 1st
hour = 5°C × 1 = 5°C
Room Temperature after 2nd
hour = 5°C × 2 = 10°C
Room Temperature after 3rd
hour = 5°C × 3 = 15°C
Room Temperature after 4th
hour = 5°C × 4 = 20°C
hour = 5°C × 5 = 25°C
hour = 5°C × 6 = 30°C
hour = 5°C × 7 = 35°C
hour = 5°C × 8 = 40°C
hour = 5°C × 9 = 45°C
hour = 5°C × 10 = 50°C
∴ the temperature of room after 10 hours is = 40°C - 50°C = (- 10°C)
7. In a class test containing 10 questions, 5 marks are awarded for every correct
answer and (–2) marks are awarded for every incorrect answer and 0 for
questions not attempted.
Total no. questions the examination contains = 10 questions
Marks awarded for each correct answer = 5 marks
Marks awarded for each incorrect answer = (- 2) marks
(i) Mohan gets four correct and six incorrect answers. What is his score?

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Answer:
Marks awarded for 4 correct answers by Mohan = 4 × 5 = 20 Marks
Marks awarded for 6 incorrect answers = 6 × (- 2) = (- 12)
Score of Mohan
= 20 + (- 12)
= 20 - 12
= 8
∴ 8 marks are the total score of Mohan in the class test.
(ii) Reshma gets five correct answers and five incorrect answers, what is her
score?
Answer:
Marks awarded for 5 correct answers by Mohan = 5 × 5 = 25 Marks
Score of Reshma
= 25 + (- 10)
= 25 - 10
= 15
∴ 15 marks are the total score of Reshma in the class test.
(iii) Heena gets two correct and five incorrect answers out of seven questions
she attempts. What is her score?
Answer:
Marks awarded for 2 correct answers by Heena = 2 × 5 = 10 Marks
Score of Heena,
= 10 + (- 10)
= 10 - 10
= 0
∴0 marks is the total score of Heena in the class test.
8. A cement company earns a profit of ₹ 8 per bag of white cement sold and a
loss of ₹ 5 per bag of grey cement sold.
Profit on per bag of white cement = ₹ 8 per bag
Loss on per bag of grey cement = ₹ 5 per bag
(a) The company sells 3,000 bags of white cement and 5,000 bags of grey cement
in a month. What is its profit or loss?
Answer:
We, denote profit by a positive integer and loss by a negative integer

24
Profit on selling 3000 bags of white cement = ₹ 8 × 3000 = ₹ (24000)
Loss on selling 5000 bags of grey cement = ₹ 5 × 5000 = ₹ (- 25000)
So,
24,000 + (- 25,000)
= 24,000 - 25,000
= (- 1000)
Therefore there is a loss of ₹1000 in total.
(b) What is the number of white cement bags it must sell to have neither profit
nor loss, if the number of grey bags sold is 6,400 bags.
Answer:
We, denote profit in Positive Integer and loss in Negative Integer.
As,
Cement Company earns a profit of ₹ 8 on per bag of white cement.
Let the number of cement bag (y)
Then,
Cement company earns a profit on selling y bags of white cement = (y) × ₹ 8
= ₹ 8x
Loss on selling 1 bag of grey cement = – ₹ 5 per bag
Then,
Loss on selling 6400 bags of grey cement = 6400 × – ₹ 5
= (– ₹ 32000)
Now let’s come to the question,
Company must sell to have neither profit nor loss.
= Profit + loss = 0
= 8x + (-32000) =0
By sending (- 32000) from L.H.S to R.H.S it becomes 32000
= 8y = 32000
= y = 32000 ÷ 8
= 4000
Hence, 4000 bags of white cement have to be sold to have neither profit nor loss for
the Cement Company.
9. Replace the blank with an integer to make it a true statement.
(a) (–3) × _____ = 27
Answer:
Let’s name the missing place (m)
So,
= (- 3) × m = 27
= (m) = 27÷ (- 3)

25
= 27 ÷ (- 3)
= (- 9)
= (- 3) × (- 9) = 27
Let’s substitute the value of (m)
(- 3) × (- 9) = 27
(b) 5 × _____ = –35
Answer:
So,
= 5 × m = (- 35)
= m = (- 35) ÷ 5
= (- 35) ÷ 5
= (- 7)
= 5 × (- 7) = (- 35)
5 × (- 7) = (- 35)
Therefore, (-7) is the answer.
(c) _____ × (– 8) = –56
Answer:
So,
= (m) × (- 8) = (- 56)
= (m) = (- 56) ÷ (- 8)
= (- 56) ÷ (- 8)
= 7
7 × (- 8) = (- 56)
(d) _____ × (–12) = 132
Answer:
So,
= (m) × (- 12) = 132
= (m) = 132 ÷ (- 12)
= (- 11)
(- 11) × (- 12) = 132

26
Exercise 1.4 (Page no. 26)
1. Evaluate each of the following:
(a) (–30) ÷ 10
Answer:
10 - 30 3
30 Therefore, (- 3) is the answer.
00
Rule of division of Integers: When we divide a negative integer by a positive integer,
we first divide them as whole numbers and then put minus sign (-) before the quotient.
(b) 50 ÷ (- 5)
Answer:
-5 50 - 10
- 5
00
00
00
(c) (- 36) ÷ (- 9)
Answer:
-9 - 36 4
36
00
(c) (- 36) ÷ (- 9)
Answer:
= (- 36) ÷ (- 9)
= 4 Therefore 4 is the answer
Rule of division of integers: When we divide a Negative integer by a Negative integer
we will first divide them as whole numbers and the put Plus sign (+) before the
quotient.
(d) (– 49) ÷ (49)
Answer:

27
= (- 49) ÷ 49
= 1 Therefore 1 is the answer.
Rule of division of integers: When we divide a Negative integer by a Positive integer
quotient.
(e) 13 ÷ [(–2) + 1]
Answer:
= 13 ÷ [(–2) + 1]
First we will solve the numbers in bracket.
= (- 2) + 1
= (- 1)
= 13 ÷ (- 1)
= (- 13) Therefore, the answer is (- 13)
(f) 0 ÷ (–12)
Answer:
= 0 ÷ 12
= 0 Therefore, the answer is 0
Rule of division of Integers: When we divide zero by a negative integer gives zero.
(g) (–31) ÷ [(–30) + (–1)]
Answer:
= (–31) ÷ [(–30) + (–1)]
First we will solve the numbers in the bracket
= (- 30) + (- 1)
= (- 30) - 1
= (- 31)
Now,
= (- 31) ÷ (- 31)
= 1 Therefore, the answer is 1
quotient.
(h) [(–36) ÷ 12] ÷ 3
Answer:
First we will solve the numbers in the brackets

28
= [(–36) ÷ 12]
= (- 3)
Rule of Division of Integers: When we divide a negative integer by a positive integer,
Now,
= (- 3) ÷ 3
= (- 1) Therefore the answer is (- 1)
(i) [(– 6) + 5)] ÷ [(–2) + 1]
Answer:
= [(– 6) + 5)] ÷ [(–2) + 1]
= (- 6) + 5
= (- 1)
Now,
= (- 2) + 1
= (- 1)
= (- 1) ÷ (- 1)
= 1 Therefore the answer is (- 1)
quotient.
2. Verify that a ÷ (b + c) ≠ (a ÷ b) + (a ÷ c) for each of the following values of a, b
and c.
(a) a = 12, b = – 4, c = 2
Answer:
From the question we understand that, a ÷ (b + c) ≠ (a ÷ b) + (a ÷ c)
We know that,
A = 12, b = (- 4), c = 2
We will consider the L.H.S (Left hand side) = a ÷ (b + c)
= 12 ÷ [(- 4) + 2]
First we will solve the numbers in the brackets.
= [(- 4) + 2]
= (- 4) + 2
= (- 2)
= 12 ÷ (- 2)
= (- 6)

29
We will now consider the R.H.S (a ÷ b) + (a ÷ c)
= [(12 ÷ (- 4)] + (12 ÷ 2)
= 12 ÷ (- 4)
= (- 3)
Now,
= 12 ÷ 2
= 6 + (- 3)
= 6 - 3
= 3
By comparing L.H.S and R.H.S
Therefore, L.H.S ≠ R.H.S
a ÷ (b + c) ≠ (a ÷ b) + (a ÷ c)
Therefore the equation is verified.
(b) a = (–10), b = 1, c = 1
Answer:
From the question we understand that, a ÷ (b + c) ≠ (a ÷ b) + (a ÷ c)
a = (–10), b = 1, c = 1
We will consider the L.H.S
= a ÷ (b + c)
= (- 10) ÷ [1 + 1]
= (- 10) ÷ 2
= (- 5)
Now,
We will consider the R.H.S
= (- 10) ÷ 1
= (- 10)
= (- 10) ÷ 1
= (- 10) ÷ (- 10)
= 1
quotient.
By comparing L.H.S and R.H.S
Therefore, L.H.S ≠ R.H.S

30
a ÷ (b + c) ≠ (a ÷ b) + (a ÷ c)
Therefore the equation is verified.
3. Fill in the blanks:
(a) 369 ÷ _____ = 369
Answer:
Then,
= 369 ÷ (m) = 369
= (m) = (369 ÷ 369)
= 1
Therefore the value of (m) is 1
That means 369 ÷ 1 = 369
(b) (–75) ÷ _____ = –1
Answer:
Then,
= (- 75) ÷ m = (- 1)
= m = [(- 75) ÷ (- 1)
= 75
Therefore the value of (m) is 75
That means (–75) ÷ 75 = –1
(c) (–206) ÷ _____ = 1
Answer:
Then,
= (–206) ÷ m = 1
= (m) = [(- 206) ÷ 1)]
= (- 206)
Therefore the value of (m) is (- 206)
That means (–206) ÷ (- 206) = 1
(d) – 87 ÷ _____ = 87
Answer:
Then,
= (- 87) ÷ m = 87
= (m) = [(- 87) ÷ 87]

31
= (- 1)
That means (- 87) ÷ (- 1) = 87
(e) _____ ÷ 1 = – 87
Answer:
Then,
= m ÷ 1 = – 87
= m = [(- 87) ÷ 1]
= (- 87)
That means (- 87) ÷ 1 = (- 87)
(f) _____ ÷ 48 = –1
Answer:
Then,
= (m) ÷ 48 = –1
= (m) = [48 ÷ (- 1)]
= (- 48)
That means (- 48) ÷ 48 = (- 1)
(g) 20 ÷ _____ = –2
Answer:
Then,
= 20 ÷ (m) = (- 2)
= (m) = [20 ÷ (- 2)]
= (- 10)
That means 20 ÷ (- 10) = –2
(h) _____ ÷ (4) = –3
Answer:
Then,
= (m) ÷ (4) = (- 3)
= (m) = (4) x (- 3)

32
= (- 12)
That means (- 12) ÷ (4) = (- 3)
4. Write five pairs of integers (a, b) such that a ÷ b = –3. One such pair is (6, –2)
because 6 ÷ (–2) = (–3).
Answer:
There are many such pairs some of them are given below
1. 15 ÷ (- 5)
As => 15 ÷ (- 5) = (- 3)
2. (- 15) ÷ 5
As => (- 15) ÷ 5 = (- 3)
3. (- 21) ÷ 7
As => (- 21) ÷ 7 = (- 3)
4. 12 ÷ (- 4)
As => 12 ÷ (- 4) = (- 3)
5. 33 ÷ (- 11)
As => 33 ÷ (- 11) = (- 3)
5. The temperature at 12 noon was 10o
C above zero. If it decreases at the rate of
2o
C per hour until midnight, at what time would the temperature be 8°C below
zero? What would be the temperature at mid-night?
Answer:
The Temperature at 12 noon = 10o
C above zero (10o
C)
The rate of decreasing per hour = 2o
C per hour
So,
Temperature at 12 noon = 10o
C
Temperature at 1 pm = 10 + (- 2)
= 10o
C + (- 2o
C)
= 10o
C - (- 2o
C)
= 8o
C
Temperature at 2 pm = 8o
C + (- 2o
C)
= 8o
C + (- 2o
C)
= 8o
C - 2o
C
= 6o
C
C + (- 2o
C)
= 6o
C + (- 2o
C)
= 6o
C - 2o
C
= 4o
C
C + (- 2o
C)

33
= 4o
C + (- 2o
C)
= 4o
C - 2o
C
= 2o
C
C + (-2o
C)
= 2o
C + (-2o
C)
= 2o
C -2o
C
= 0o
C
C + (-2o
C)
= 0o
C + (-2o
C)
= 0o
C -2o
C
= (-2o
C)
Temperature at 7 pm = (- 2o
C) + (- 2o
C)
= (- 2o
C) + (- 2o
C)
= (- 2o
C) - 2o
C
= (- 4o
C)
C) + (- 2o
C)
= (- 4o
C) + (- 2o
C)
= (- 4o
C) - 2o
C
= (- 6o
C)
C) + (- 2o
C)
= (- 6o
C) + (- 2o
C)
= (- 6o
C) - 2o
C
= (- 8o
C)
C) + (- 2o
C)
= (- 8o
C) + (- 2o
C)
= (- 8o
C) - 2o
C
= (- 10o
C)
C) + (- 2o
C)
= (- 10o
C) + (- 2o
C)
= (- 10o
C) - 2o
C
= (- 12o
C)
Temperature at 12 pm = (- 12 o
C) + (- 2o
C)
= (- 12o
C) + (- 2o
C)
= (- 12o
C) - 2o
C
= (- 14o
C)
8o
C below 0 means (- 8o
C)
Therefore at 9 pm the temperature would be 8o
C below 0 (i.e. (- 8o
C)
The temperature at midnight is (- 14o
C).

34
6. In a class test (+ 3) marks are given for every correct answer and (–2) marks
are given for every incorrect answer and no marks for not attempting any
question.
(i) Radhika scored 20 marks. If she has got 12 correct answers, how many
questions has she attempted incorrectly?
Answer:
Marks given for every correct answer = (+ 3) marks
Marks given or every incorrect answer = (- 2) marks
(i)
Score of Radhika = 20 marks
Marks awarded for 12 correct answers = 12 x 3 = 36 marks
No. of questions attempted incorrectly = Total score - Marks awarded for correct
answers
= 20 - 36
= (- 16)
So,
Incorrect answers answered by Radhika = (- 16) ÷ (- 2)
= 8
Therefore Radhika answered 8 incorrect answers.
(ii) Mohini scores –5 marks in this test, though she has got 7 correct answers.
How many questions has she attempted incorrectly?
Answer:
Marks given for every correct answer = (+ 3) marks
Marks given or every incorrect answer = (- 2) marks
(ii) Answer
Score of Mohan = (- 5) marks
Marks awarded for 7 correct answers = 7 x 3 = 21 marks
No. of questions attempted incorrectly = Total score - Marks awarded for correct
answers
= (- 5) - 21
= (- 26)
So,
Incorrect answers answered by Mohini = (- 26) ÷ (- 2)
= 13
Therefore Mohini answered 13 incorrect answers.
7. An elevator descends into a mine shaft at the rate of 6 m/min. If the
Descend starts from 10 m above the ground level, how long will it take to reach –
350 m.

35
Answer:
Depth of the elevator is denoted by a negative integer
Speed by which elevator is descending = 6 m/min
Time it will take to reach 350 m above =
As it was 10 m above the ground = 350m - 10m = 360m
So,
360m ÷ 6
= 60
Because,
Time taken by the elevator to descend -6 m = 1 min
So, time taken by the elevator to descend – 360 m = (-360) ÷ (-60)
= 60 minutes
= 1 hour

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