The document outlines various mathematical shortcuts for calculating percentages, changes in value, and profits or losses in different scenarios. It includes examples for calculating overall percentage changes from increment and decrement, as well as applications in business, such as profit-sharing among partners and cost-price calculations. The document serves as a resource for improving mathematical aptitude in real-world contexts.

1. Mathematical Shortcuts
for
Aptitude
Pawan mishra
Aptitude Trainer

2. Percentage
• increased by x % then decreased by y % then resulting
effect in percent :
• +x – y –
• Increased by x% then again increased by y% then
• +x+y+
• Decreased by x% then increased by y%
• –x+y –
• Decreased by x% then again decreased by y%
• – x – y +
•
If the value of something is

3. Example – 1
• The Salary of a worker is first increased by 10%
and thereafter decreased by 5%.
• What is the overall change in percent.
• overall change = + 10 - 5 + (+10)(-5)/100
• = + 4.5 % (increased)
• use (+) sign for increment and (-) sign for
decrement.

4. Example – 2
• A shopkeeper marks the price of goods 20%
more than the real price. He allowed a
discount of 10%.What profit or loss did he
get?
• Profit or loss the shopkeeper get:
• 20 - 10 + (+20)(-10)/100 = + 8% (profit)

5. Example 3
• The side of a square is increased by 30%. Find
the percentage increase in area.
• Increase in area = 30 + 30 + (30)(30)/100 =
69%.

6. Example 4
• If the radius of a circle is decreased by 20%.
What percent change in area?
• percent change in area:
• - 20 - 20 + (-20)(-20)/100 = -36% (decreased)

7. Example 5
• If the price of a shirt is increased by 15% than
decreased by 15%. What is percent change?
• percent change :
• + 15 - 15 + (+15)(-15)/100 = - 2.25 %
(decreased)

8. Example 6
• The length of a rectangle is increased by 40%
and breadth is decreased by 40%. Find change
in area.
• percent change in area:
• 40 - 40 + (-40)(+40)/100 = -16%(decreased)

9. Example 7
• if a number is increased by 20% and again
increased by 20%. By what percent should the
number increased.
• percent increased:
• 20 + 20 + (+20)(+20)/100 = 44%(increased)

10. Percentage – 2
• If the price of the commodity is increased or
decreased by r% then reduction in the
consumption so as not to increase the
expenditure :
•

11. Example 1
• If the price of the sugar fall down by 10%. By
how much percent must the householder
increase its consumption so as not to
decrease the expenditure.
• increase in consumption :
•

12. Example 2
• If A's salary is 25% more than B then how
much percent the B's salary is less than that of
A.
• B's salary is less than that of A :
•
•

13. Example 3
• If the price of petrol is increased by 30
percent, by how much petrol a car owner
must reduce his consumption in order to
maintain the same budget.
• reduction in consuption :
•

14. Percentage – 3
• x% of a quantity is taken by the first, y% of the
remaining is taken by the second and so on,
• Now if A is the amount left then find the initial
amount :
• initial amount =
• where A is the left amount.
•

15. Example 1
• After reducing 10% from a certain sum and
then 20% from the remaining , there is Rs3600
left then find the original sum.
• original sum =
• =3600 X = Rs.5000.
•

16. Example 2
• In a library 20% of the books are in hindi , 50%
of the remaining are in English 30% of the
remaining are in french, the remaining 6300
books are in regional language, total no of
books would be?
• Total no of books = 6300X=22500
•

17. Percentage – 4
• A candidate scoring x% in an examination fails
by 'a' marks, while another candidate who
scores y% marks gets 'b' marks more than
then the minimum required pass marks.
• Then the maximum marks for the examination
are
•

18. Example
• A candidate scores 25% and fails by 30 marks,
while another candidate who scores 50%
marks, gets 20 marks more than the minimum
required marks to pass the examination.
• Find the maximum marks for the examination.
• Maximum marks = 100X =200.
•

19. Percentage – 5
• If 'a' articles are bought for Rs 'b' and sell
them 'c' for Rs 'd'. Then profit or loss made by
the vendor:
•

20. Example 1
• If a man purchase 11 orange for Rs 10 and sell
them 10 for Rs 11. How much profit or loss did
he made?
• Profit or loss made = X100 =21% profit.
•

21. Example 2
• A boy buys orange 9 for Rs 16 and sell them
11 for Rs 20. Find profit or loss percent.
• profit or loss percent made :
•

22. Percentage – 6
• Selling Price(SP) = given(Rs) X
• By selling a horse for Rs 570 a trader loses 5%.
At what price must he sell it to gain 5%.
• Selling Price = 570 X =Rs.630
•

23. Percentage – 7
• Cost Price(CP) = X 100
• Mahesh sold a book at a profit of 12%. Had he
sold it for Rs 18 more , 18% would have been
gained. Find CP.
• Cost Price = =Rs.300.
•

24. Example 2
• A man sold a horse at a loss of 7%. Had he be
able to sell it at a gain of 9%. It would have
fetch 64 more. Find Cost Price.
• Here difference in Percent is 9 - (-7) = 16
• Cost Price = =Rs.400
•

25. Simple Interest – 1
• Principal =
• A sum was put at SI at a certain value for 2
years, had it been put at 3% higher rate, it
would have fetch 300 more , find the sum.
• Principal = Rs.5000.
•

26. Simple Interest – 2
• Time = given time X
• A sum of money double itself in 4 years , in
how many years will it become 8 times of
itself ?
• Time = 4 X =28 years
•

27. Example 2
• A sum of money double itself in 7 years , in
how many years it will become 4 times of
itself?
• Time = =21 years.
•

28. S.I & C.I
• If the difference between Simple Interest and
Compound Interest on a certain sum of money for
2 years at R% rate is given then
If the difference between simple interest and compound interest on a certain sum
of money at 10% per annum for 2 years is Rs 2 then find the sum.

29. S.I & C.I
• If the difference between Simple Interest and
Compound Interest on a certain sum of money
for 3 years at R% is given then
If the difference between simple interest and compound interest on a certain sum
of money at 10% per annum for 3 years is Rs 2 then find the sum.
Sol:

30. COMPOUND INTEREST
• If sum A becomes B in T1 years at compound interest, then
after T2 years
Rs 1000 becomes 1100 after 4 years at
certain compound interest rate. What will
be the sum after 8 years?
Sum:
Here A = 1000, B = 1100
T1 = 4, T2 = 8

31. Ratio / Proportion 2
• If A is x% of C and B is y% of C then A is x100%
of B
• Two numbers are respectively 20% and 25% of
a third number, what percentage is the first of
the second.
• =80%
•

32. Partnership – 1
If two partners are investing their money C1 and C2
for equal period of time and their total profit is P then
their shares of profit are
If these partners are investing their money for
different period of time which is T1 and T2, then their
profits are

33. Partnership – 2
Jack and Jill start a business by investing $ 2,000 for 8 months and $
3,000 for 6 months respectively. If their total profit si $ 510 and then
what is profit of Jill?
Let’s Say C1 = 2000, T1 = 8
C2 = 3000, T2 = 6
P = 510

34. Partnership – 3
If n partners are investing their money C1, C2, …, Cn for
equal period of time and their total profit is P then their
shares of profit are
If these partners are investing their money for different
period of time which is T1, T2,… , Tn then their profits are

35. Example 1
Raju, Kamal and Vinod start a business by investing Rs 5,000 for 12 months,
Rs 8,000 for 9 months and Rs 10,000 for 6 months. If at the end of the year
their total profit is Rs 2000 then find the profit of each partner.
Let’s Say C1 = 5000, T1 = 12
C2 = 8000, T2 = 9
C3 = 10000, T3 = 6
P = 2000

37. Time & Distance 1
• If different distance is travelled in different
time then,
If a car travels 50 Km in 1 hour, another 40 Km in 2 hour and another 70 Km in
3 hour then what is average speed of car.
Total Distance Covered = 50 + 40 + 70 = 160 Km
Total Time Taken = 1 + 2 + 3 = 6 hours.

38. Time & Distance 2
• If equal distance is travelled at different speed.
• If equal distance is travelled at the speed of A and B then,
A boy goes to his school which is 2 Km away in 10
minutes and returns in 20 mins then what is boy’s
average speed.
Let’s say A = 2/10 = 0.2 km/min
And B = 2/20 = 0.1 km/min
If the same distance is covered at two different speeds S1 and
S2 and the time taken to cover the distance are T1 and T2, then
the distance is given by

39. Time & Distance 3
• If equal distance is travelled at the speed of A, B
and C then,
If a car divides its total journey in three equal parts and
travels those distances at speed of 60 kmph, 40 kmph and 80
kmph then what is car’s average speed?
Let’s say A = 60, B = 40 and C = 80, then
Average Speed =
=
= 55.38

41. Decimal Equivalent of Fractions
• With a little practice, it's not hard to recall the decimal equivalents of fractions up to
• 10/11!
• First, there are 3 you should know already:
• 1/2 = .5
• 1/3 = .333...
• 1/4 = .25
• Starting with the thirds, of which you already know one:
• 1/3 = .333...
• 2/3 = .666...
• You also know 2 of the 4ths, as well, so there's only one new one to learn:
• 1/4 = .25
• 2/4 = 1/2 = .5
• 3/4 = .75

42. • Fifths are very easy. Take the numerator (the number on top), double it, and stick a
• decimal in front of it.
• 1/5 = .2
• 2/5 = .4
• 3/5 = .6
• 4/5 = .8
• There are only two new decimal equivalents to learn with the 6ths:
• 1/6 = .1666...
• 2/6 = 1/3 = .333...
• 3/6 = 1/2 = .5
• 4/6 = 2/3 = .666...
• 5/6 = .8333...
• What about 7ths? We'll come back to them at the end. They're very unique.
• 8ths aren't that hard to learn, as they're just smaller steps than 4ths. If you have trouble with any of the
8ths, find the nearest 4th, and add .125 if needed:

43. • 1/8 = .125
• 2/8 = 1/4 = .25
• 3/8 = .375
• 4/8 = 1/2 = .5
• 5/8 = .625
• 6/8 = 3/4 = .75
• 7/8 = .875
• 9ths are almost too easy:
• 1/9 = .111...
• 2/9 = .222...
• 3/9 = .333...
• 4/9 = .444...
• 5/9 = .555...
• 6/9 = .666...
• 7/9 = .777...
• 8/9 = .888...
• 10ths are very easy, as well. Just put a decimal in front of the numerator:
• 1/10 = .1
• 2/10 = .2
• 3/10 = .3
• 4/10 = .4
• 5/10 = .5
• 6/10 = .6
• 7/10 = .7
• 8/10 = .8
• 9/10 = .9
• Remember how easy 9ths were? 11th are easy in a similar way, assuming you know your multiples of 9:
• 1/11 = .090909...
• 2/11 = .181818...
• 3/11 = .272727...
• 4/11 = .363636...
• 5/11 = .454545...
• 6/11 = .545454...
• 7/11 = .636363...
• 8/11 = .727272...
• 9/11 = .818181...
• 10/11 = .909090...
• As long as you can remember the pattern for each fraction, it is quite simple to work out

44. • Oh, I almost forgot! We haven't done 7ths yet, have we?
• One-seventh is an interesting number:
• 1/7 = .142857142857142857...
• For now, just think of one-seventh as: .142857
• See if you notice any pattern in the 7ths:
• 1/7 = .142857...
• 2/7 = .285714...
• 3/7 = .428571...
• 4/7 = .571428...
• 5/7 = .714285...
• 6/7 = .857142...
• Notice that the 6 digits in the 7ths ALWAYS stay in the same order and the starting digit is the only thing that changes!
• If you know your multiples of 14 up to 6, it isn't difficult to work out where to begin the decimal number. Look at this:
• For 1/7, think "1 * 14", giving us .14 as the starting point.
• For 2/7, think "2 * 14", giving us .28 as the starting point.
• For 3/7, think "3 * 14", giving us .42 as the starting point.
• For 4/14, 5/14 and 6/14, you'll have to adjust upward by 1:
• For 4/7, think "(4 * 14) + 1", giving us .57 as the starting point.
• For 5/7, think "(5 * 14) + 1", giving us .71 as the starting point.
• For 6/7, think "(6 * 14) + 1", giving us .85 as the starting point.
• Practice these, and you'll have the decimal equivalents of everything from 1/2 to 10/11 at
• your finger tips!

45. Rule of Alligation
• If two ingredients are mixed, then
• C.P of a unit quantity of cheaper = (c)
• C.P of a unit quantity of dearer = (d)
•
C D
D–M M–C
Mean
Price (m)

46. • 2.In what ratio must a grocer mix two varieties of
pulses costing `.15 and `.20 per kg respectively so
as to get a mixture worth `.16.50 kg?
First type Mean Price Second type
15 16.50 20
3.50 1.50

47. • 4. A jar full of whisky contains 40% alcohol. A part of
this whisky is replaced by another containing 19%
alcohol and now the percentage of alcohol was
found to be 26%. The quantity of whisky replaced is:
First Mean Price Second type
40% 26% 19%
7 14
The ratio is 7:14 = 1:2.
Hence quantity replaced =

48. • 5.In what ratio must water be mixed with milk
to gain on selling the mixture at cost price?
• Let C.P. of 1 litre milk be Re. 1.
• S.P. of 1 litre of mixture = Re.1,
• C.P. of 1 litre of mixture =
•
First type Mean Price Second type
0 1
First type Mean Price Second type
0 1
Ratio of water and milk = 1:6.

49. • A milkman has 10 litres of pure milk. How many
litres of water have to be added to the milk so
that the milk man gets a profit of 150% by
selling at cost price?
• The ratio of water and milk is 3:2.
• Hence 15 litres of water should be added.
•
First type Mean Price Second type
0 1
First type Mean Price Second type
0 1

50. • If n different vessels of equal size are filled with the mixture of P
and Q in the ratio p1 : q1, p2 : q2, ……, pn : qn and content of all
these vessels are mixed in one large vessel, then

51. • Three equal buckets containing the mixture of milk and water are mixed into a bigger bucket.
• If the proportion of milk and water in the glasses are 3:1, 2:3 and 4:2 then find the proportion of milk
and water in the bigger bucket.
Sol:
• Let’s say P stands for milk and Q stands for water,
So, p1:q1 = 3:1
p2:q2=2:3
p3 : q3=4:2
So in bigger bucket,
Milk : Water = 109 : 71

52. • If n different vessels of sizes x1, x2, …, xn are
filled with the mixture of P and Q in the ratio
p1 : q1, p2 : q2, ……, pn : qn and content of all
these vessels are mixed in one large vessel,
then

53. • Three buckets of size 2 litre, 4 litre and 5 litre containing the mixture of milk and
water are mixed into a bigger bucket. If the proportion of milk and water in the
glasses are 3:1, 2:3 and 4:2 then find the proportion of milk and water in the bigger
bucket.
Sol:
• Let’s say P stands for milk and Q stands for water,
So, p1:q1 = 3:1 , x1 = 2
p2:q2=2:3 , x2 = 4
p3 : q3=4:2 x3 = 5, so
So in bigger bucket,
Milk : Water = 193 : 137

54. • Suppose a container contains x of liquid from which y
units are taken out and replaced by water. After n
operations, the quantity of pure liquid = units.
• A container contains 40 litres of milk. From this container
4 litres of milk was taken out and replaced by water. This
process was repeated further two times. How much milk
is now contained by the container?
• Milk =
•

55. • p gram of ingredient solution has a% ingredient in it.
• To increase the ingredient content to b% in the solution

56. • 125 litre of mixture of milk and water contains 25% of water.
How much water must be added to it to make water 30% in
the new mixture?
Sol:
• Let’s say p = 125, b = 30, a = 25
So from the equation
Quantity of water need to be added = 8.92 litre.

57. • If in x litres mixtures of milk and water, the ratio of
milk and water is a:b, the quantity of water to be
added in order to make this ratio c:d is
1. In a mixture of 60 litres, the ratio of milk and water is 2:1. If
this ratio is to be 1:2, then the quantity of water to be
further added is a) 20 litres. b) 30 litres c) 40 litres d) 60
litres.
=
•
( )
( )
x ad bc
c a b
−
+

58. • 11. A vessel is filled with liquid, 3 parts of
which are water and 5 parts syrup. How much
of the mixture must be drawn off and
replaced with water so that the mixture may
be half water and half syrup?
• Old ratio 3:5 new ratio 1:1
• Qty of water to be added =
•

59. • 1. A milk vendor has 2 cans of milk. The first contains 25% water and
the rest milk. The second contains 50% water. How much milk should
he mix from each of the containers so as to get 12 litres of milk such
that the ratio of water to milk is 3:5.
• For the first the old ratio 1:4. new ratio 3:5
• Amount of milk should be added=
• For the second the old ratio 1:1. new ratio 3:5
• Amount of milk should be added=
• Totally litres of milk should be added to get 12 litres of milk.
•

60. LCM – MODEL 1
• Any number which when divided by p,q or r leaving the same remainder s in
each case will be of the form
• k (LCM of p, q and r)+ s where k = 0,1,2…
• If we take k = 0, then we get the smallest such number.
• Example:
• The least number which when divided by 5,6,7 and 8 leaves a remainder 3,
but when divided by 9 leaves no remainder, is:
• K(LCM of 5,6,7 and 8) + 3 = 840k + 3
• Least value of k for which 840k + 3 divisible by 9 is
• K=2.
• Required number is 1683.

61. LCM MODEL 2
• Any number which when divided by p,q or r leaving respective
remainders of s, t and u where (p–s) = (q – t) = ( r – u) -= v (say) will
be of the form
• K(LCM OF P, Q AND R) – V
• The smallest such number will be obtained by substituting k = 1.
• Example:
• Find the smallest number which when divided by 4 and 7 gives
remainders of 2 and 5 respectively.
• LCM OF 4 AND 7 IS 28.
• HENCE 28 – 2 = 26.

62. LCM MODEL 3
• Find the smallest number which when divided by 7
leaves a remainder of 6 and when divided by 11 leaves a
remainder of 8.
• The required number will be 11k + 8
• When divided by 7 leaves a remainder 6.
• Subtracting 6 from 11k + 8 we have 11k + 2 which
should be multiple of 7.
• By trial, when k =3, we get 35.
• Hence Required number is when k = 3, 11k+8 = 41.

63. HCF MODEL 1
• The largest number with which the
numbers p,q or r are divided giving
remainder of s, t and u respectively
will be the HCF of the three numbers
of the form (p – s), (q – t) and (r – u)
• Example
• Find the largest number with which
when 906 and 650 are divided they
leave remainders 3 and 5.
• The HCF of (906 – 3) and
( 650 – 5).
• HCF of 903 and 645 is 129.
645) 903(1
645
––––
258
258)645(2 129)258(2
516
–––––
129
258
–––––
0

64. HCF MODEL 2
• The largest number which when we divide by the
numbers p,q and r , the remainders are the same is
• HCF of (p – r) and (q – r) where r is the smallest among
the three.
• Example
• Find the greatest number that will divide 43, 91 and 183
so as to leave the same remainder in case.
• Required number = H.C.F of (91 – 43), and (183 – 43) =
H.C.F of 48 and 140 is 4.

65. LAST DIGIT OF ANY POWER
• Last digit of 21 is 2
• Last digit of 22 is 4
• Last digit of 23 is 8
• Last digit of 24 is 6
• Last digit of 25 is 2
• Last digit of 31 is 3
• Last digit of 32 is 9
• Last digit of 33 is 7
• Last digit of 34 is 1
• Last digit of 35 is 3

66. Digit
s
Powers
1 1 2 3 4 5 6 7 8 9
2 2 4 8 6 2 4 8 6 2
3 3 9 7 1 3 9 7 1 3
4 4 6 4 6 4 6 4 6 4
5 5 5 5 5 5 5 5 5 5
6 6 6 6 6 6 6 6 6 6
7 7 9 3 1 7 9 3 1 7
8 8 4 2 6 8 4 2 6 8
9 9 1 9 1 9 1 9 1 9
For every digit unit place digits of increasing powers repeat after 4th power.
This means unit place digit for power=5 is same as unit place digit for power=1 for
every number.
2) For digits 2, 4 & 8 any power will have either 2 or 4 or 6 or 8 at unit place.
3) For digits 3 & 7 any power will have either 1 or 3 or 7 or 9 at unit place.
4) For digit 9 any power will have either 1 or 9 at unit place.
5) And for digits 5 & 6 every power will have 5 & 6 at unit place respectively.

67. LARGEST POWER OF A NUMBER IN N!
• Find the largest power of 5 that
can divide 216! without leaving
any remainder. (or)
• Find the largest power of 5
contained in 216!
• Add all the quotients to get 43 +
8 + 1 = 52.
• Therefore 552 is the highest
power of 5 contained in 216!
5 216  Number given
5 43  Quotient 1
5 8  Quotient 2
1  Quotient 3
Please note that this method is
applicable only when the number
whose largest power is to be found
out is a prime number.
If it is not a prime number, then split
the number as product of primes and
find the largest power of each factor.
Then the smallest amoung the largest
poser of these relative factors of the
given number will the largest power
required.

68. an – bn
• It is always divisible by a – b.
• When n is even it is also divisible by a + b.
• When n is odd it is not divisible by a + b.

69. an + bn
• It is never divisible by a – b.
• When n is odd it is also divisible by a + b.
• When n is even it is not divisible by a + b.

70. • There are three departments having students
64,58,24 .In an exam they have to be seated in
rooms such that each room has equal number
of students and each room has students of
one type only (No mixing of departments. Find
the minimum number rooms required ?
• The HCF is 2. Hence 32 + 29 + 12= 73.

71. Calendar

72. Odd Days
• We are supposed to find the day of the week
on a given date.
• For this, we use the concept of 'odd days'.
• In a given period, the number of days more
than the complete weeks are called odd days.

73. Leap Year
• (i). Every year divisible by 4 is a leap year, if it is not a century.
• (ii). Every 4th century is a leap year and no other century is a leap year.
• Note: A leap year has 366 days.
• Examples:
• Each of the years 1948, 2004, 1676 etc. is a leap year.
• Each of the years 400, 800, 1200, 1600, 2000 etc. is a leap year.
• None of the years 2001, 2002, 2003, 2005, 1800, 2100 is a leap year.
• Ordinary Year:
• The year which is not a leap year is called an ordinary years. An ordinary year
has 365 days.

74. Counting of odd days
• 1 ordinary year = 365 days = (52 weeks + 1 day.)
• 1 ordinary year has 1 odd day.
• 1 leap year = 366 days = (52 weeks + 2 days)
• 1 leap year has 2 odd days.
• 100 years = 76 ordinary years + 24 leap years
• = (76 x 1 + 24 x 2) odd days
• = 124 odd days.
• = (17 weeks + days) 5 odd days.
• Number of odd days in 100 years = 5.
• Number of odd days in 200 years = (5 x 2) 3 odd days.
• Number of odd days in 300 years = (5 x 3) 1 odd day.
• Number of odd days in 400 years = (5 x 4 + 1) 0 odd day.
• Similarly, each one of 800 years, 1200 years, 1600 years, 2000 years etc. has 0 odd days.

75. Day of the Week Related to Odd Days
No. of
days:
0 1 2 3 4 5 6
Day: Sun. Mon. Tues. Wed. Thurs. Fri. Sat.

76. • If 6th March 2005 is Monday, what was the day of the week on 6th
March, 2004?
• The year 2004 is a leap year. So, it has 2 odd days.
• But Feb 2004 not included because we are calculating from March
2004 to March 2005.
• So it has 1 odd day only.
• The day on 6th March, 2005 will be 1 day beyond the day on 6th
March, 2004.
• Given that, 6th March, 2005 is Monday, 6th March, 2004 is Sunday
• (1 day before to 6th March, 2005.)

77. • On what dates of April, 2001 did Wednesday fall?
• We shall find the day on 1st April,2001.
• 1st April 2001 = (2000 years + Period from 1.1.2001 to 1.4.2001)
• Odd days in 2000 years = 0
• Jan,Feb,Mar,Apr
• (31+28+31+1) = 91 days = o odd days.
• Total number of odd days = 0.
• On 1st April 2001 it was Sunday.
• In April 2001, Wednesday falls on 4th,11th,18th and 25th.

78. • The last day of a century cannot be?
• 100 years contain 5 odd days.
• Last day of 1st century is Friday.
• 200 years contain (5x2) 3 odd days.
• Last day of 2nd century is Wednesday.
• 300 years contain (5x3) 1 odd day.
• Last day of 3rd century is Monday.
• 400 years contain 0 odd day
• Last day of 4th century is Sunday.
• This cycle is repeated.
• Hence Last day of a century cannot be Tuesday or Thursday or Saturday.

79. • On 8th Feb, 2005 it was Tuesday.
• What was the day of the week on 8th Feb
2004?
• The year 2004 is a leap year. It has 2 odd days.
• The day on 8th Feb 2004 is 2 days before the
day on 8th Feb.2005.
• Hence this day is Sunday.

80. JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
0 3 3 6 1 4 6 2 5 0 3 5
Step1: Ask for the Date. Ex: 23rd June 1986
Step2: Number of the month on the list, June is 4.
Step3: Take the date of the month, that is 23
Step4: Take the last 2 digits of the year, that is 86.
Step5: Find out the number of leap years. Divide the last 2 digits of the year by 4, 86
divide by 4 is 21.
Step6: Now add all the 4 numbers: 4 + 23 + 86 + 21 = 134.
Step7: Divide 134 by 7 = 19 remainder 1.
The reminder tells you the day.
No. of
days:
0 1 2 3 4 5 6
Day: Sun. Mon. Tues. Wed. Thurs. Fri. Sat.
1600/2000 1700/2100 1800/2200 1900/2300
0 6 4 2

81. Boats – 1
• A man can row certain distance downstream
in t1 hours and returns the same distance
upstream in t2 hours. If the speed of stream is
y km/h, then the speed of man in still water is
given by

82. Boats – 2
• A man can row in still water at x km/h. In a
stream flowing at y km/h, if it takes him t
hours to row to a place and come back, then
the distance between two places is given by

83. Boats – 3
• A man can row in still water at x km/h. In a stream
flowing at y km/h, if it takes t hours more in
upstream than to go downstream for the same
distance, then the distance is given by

84. Boats – 4
• A man can row in still water at x km/h. In a stream
flowing at y km/h, if he rows the same distance up
and down the stream, then his average speed is given
by

85. Pipes & Cistern
• Pipe and Cistern problems are similar to time and work problems. A pipe is used to
fill or empty the tank or cistern.
• Inlet Pipe: A pipe used to fill the tank or cistern is known as Inlet Pipe.
• Outlet Pipe: A pipe used to empty the tank or cistern is known as Outlet Pipe.
• Some Basic Formulas
• If an inlet pipe can fill the tank in x hours, then the part filled in 1 hour = 1/x
• If an outlet pipe can empty the tank in y hours, then the part of the tank emptied
in 1 hour = 1/y
• If both inlet and outlet valves are kept open, then the net part of the tank filled in 1
hour is

86. Pipes & Cistern – 1
• Two pipes can fill (or empty) a cistern in x and y
hours while working alone. If both pipes are
opened together, then the time taken to fill (or
empty) the cistern is given by

87. Pipes & Cisterns – 2
• Three pipes can fill (or empty) a cistern in x, y
and z hours while working alone. If all the
three pipes are opened together, the time
taken to fill (or empty) the cistern is given by

88. Pipes & Cisterns – 3
• If a pipe can fill a cistern in x hours and another can fill the same
cistern in y hours, but a third one can empty the full tank in z
hours, and all of them are opened together, then

89. Pipes & Cisterns – 4
• A pipe can fill a cistern in x hours. Because of a leak in the
bottom, it is filled in y hours. If it is full, the time taken by
the leak to empty the cistern is