techniques in adding

1. Lesson 3 ADDITION
Examples
(A) Making tens and hundreds
Example 1: Add the number by making tens.
(a) 3 + 5 + 7
= 10 + 5
= 15
(b) 4 + 7 + 6
= 10 + 7
= 17
(c) 5 + 4 + 5
= 10 + 4
= 14
(d) 2 + 9 + 8
= 10 + 9
=19
(e) 4 + 5 + 6 + 5
= 10 + 10
= 20
(f) 7 + 8 + 2 + 3
= 10 + 10
= 20
Example 2: Add the numbers by making tens or hundreds.
(a) 35 + 15 + 65
=100 + 15
=115
(b) 45 + 55 + 20
= 100 + 20
= 120
(c) 38 + 22 + 16
= 60 + 16
= 76
(d) 42 + 16 + 38
= 80 + 16
= 96
(e) 15 + 32 + 48 + 5
= 80 + 20
= 100

2. (f) 17 + 13 + 25 + 35
= 30 + 60
= 90
(B) Breaking up or Rounding up numbers
Example 1: Find the value of 17 + 18 + 19.
17 + 18 + 19 = 20 – 3 + 20 – 2 + 20 – 1
= 60 – 3 – 2 – 1
=60 – 6
= 54
Example 2: Find the value of 37 + 38 + 35.
37 + 38 + 35 = 30 + 7 + 30 + 8 + 30 + 5
= 90 + 7 + 8 + 5
= 90 + 7 + 8 + 3 + 2
=90 + 20
= 110
Example 3: Find the value of 17 + 21 + 14.
17 + 21 + 14 = 17 + 3 + 11 + 21
= 20 + 32
= 52
Example 4: Find the value of 9 + 99 + 999.
9 + 99 + 999 = 10 – 1 + 100 – 1 + 1000 – 1
= 1000 + 100 + 10 – 3
= 1107

3. (C) Express a number as a sum of 2 or 3 numbers
Example 1: 2 3 5 7 11
13 17 19 23 29
Express each number below as the sum of 2 numbers given above.
(a) 10 = 7 + 3
(b) 12 = 7 + 5
(c) 18 = 5 + 13
Or
18 = 7 + 11
(d) 30 = 11 + 19
Or
30 = 13 + 17
Or
30 = 23 + 7
Example 2: 2 3 5 7 11 13
17 19 23 29 31 33
Express each number below as the sum of 3 numbers given above.
(a) 10 = 2 + 3 + 5
(b) 24 = 2 + 3 + 19
Or
24 = 2 + 5 + 17
(c) 46 = 2 + 13 + 31
Or
46 = 2 + 11 + 133
(d) 39 = 3 + 7 + 29
Or
39 = 3 + 17 + 19
a. 2 + 8 + 7
b. 5 + 4 + 6 + 5
c. 9 + 2 + 8 + 1

4. d. 14 + 16 + 21 + 29
e. 13 + 28 + 22 + 17
f. 15 + 37 + 23 + 25
g. 26 + 14 + 33 + 37
h. 18 + 19 + 22 + 11
i. 28 + 32 +15 + 25
j. 32 + 22 + 28 + 10
k. 42 + 16 + 15 + 18
l. 18 + 13 + 22 + 28
1. Find the values of the following
a. 9 + 8 + 10
b. 7 + 8 + 9
c. 7 + 8 + 11
d. 10 + 19 + 17
e. 18 + 19 + 20
f. 9 + 19 + 39
g. 18 + 28 + 38
h. 16 + 17 + 18 + 19
2. Find the values of the following.
a. 18 + 19 + 13
b. 17 + 18 + 15
c. 21 + 22 + 23 + 24
d. 19 + 17 + 14 + 21
e. 33 + 24 + 13 + 14
f. 29 + 23 + 9 + 22
g. 29 + 23 + 28 + 16
h. 27 + 4 + 29 + 35
3. 2 3 5 7 11
13 17 19 23 29
Express each number below as the sum of 2 numbers given above.
a. 7 = ( ) +( )
b. 12 = ( ) + ( )
c. 18 = ( ) + ( )
d. 36 = ( ) + ( )
36 = ( ) + ( )
36 = ( ) + ( )
e. 42 = ( ) + ( )
42 = ( ) + ( )
f. 48 = ( ) + ( )
4. Express each number as the sum of 3 numbers given in question 4.

5. a. 10 = ( ) + ( ) + ( )
b. 23 = ( ) + ( ) + ( ) + ( ) + ( ) + ( )
c. 38 = ( ) + ( ) + ( ) + ( ) + ( ) + ( )
d. 37 = ( ) + ( ) + ( ) + ( ) + ( ) + ( )
e. 41 = ( ) + ( ) + ( ) + ( ) + ( ) + ( )
f. 49 = ( ) + ( ) + ( ) + ( ) + ( ) + ( )
5. Fill in each box with the correct answer to make the addition works.
a. 3
+ 3
Solve by Comparison and Replacement
Practice
3. + = 14
- = 6
= ? = ?
4. + = 15
- = 7
= ? = ?
5. - = 22
+ = 30
= ? = ?
6. + + = 15
+ = 11
= ? = ?

6. Chapter 3
1. (a) 2 + 8 + 3 + 7 = 10 + 10
= 20
(b) 5 + 4 + 6 + 5 = 10 + 10
= 20
(c) 9 + 2 + 8 + 1 = 10 + 10
=20
(d) 14 + 16 + 21 + 29 = 30 + 30
= 80
(e) 13 + 28 + 22 + 17 = 30 + 50
= 80
(f) 15 + 37 + 23 + 25 = 60 + 40
= 100
(g) 26 + 14 + 33 + 37 = 40 + 70
= 110
(h) 18 + 19 + 22 + 11 = 40 + 30
= 70
(i) 28 + 32 + 15 + 25 = 60 + 40
= 100
(j) 32 + 22 + 28 + 10 = 32 + 50 + 10
= 92
(k) 42 + 16 + 15 + 18 = 60 + 16 + 4 + 11
= 80 + 11
= 91
(l) 18 + 13 + 22 + 28 = 18 + 2 + 11 + 50
= 20 + 11 + 50
= 81

7. 2. (a) 9 + 8 + 10 = 10 – 1 + 10 – 2 + 10
= 30 – 3
= 27
(b) 7 + 8 + 9
= 10 – 3 + 10 – 2 + 10 – 1
= 30 – 6
= 24
(c) 7 + 8 + 9 + 11 = 7 + 3 + 5 + 20
= 10 + 5 + 20
= 35
(d) 10 + 19 + 17
= 10 + 20 – 1 + 20 – 3
= 50 – 4
= 46
(e) 18 + 19 + 20
= 20 – 2 + 20 – 1 + 20
= 60 – 3
= 57
(f) 9 + 19 + 39
= 10 – 1 + 20 – 1 + 40 – 1
= 70 – 3
= 67
(g) 18 + 29 + 20
= 20 – 2 + 30 – 2 + 40 – 2
= 90 – 6
= 84

8. (h) 16 + 17 + 18 + 19
= 10 + 3 + 2 + 1 + 17 + 18 + 19
= 10 + 20 + 20 + 20
= 70
3. (a) 18 + 19 + 13 = 18 + 19 + 2 + 1 + 10
= 20 + 20 + 10
= 50
(b) 17 + 18 + 15 = 17 + 18 + 3 + 2 + 10
= 20 + 20 + 10
= 50
(c) 21 + 22 + 23 + 24
= 20 + 1 + 20 + 2 + 20 + 3 + 20 + 4
= 20 × 4 + 1 + 2 + 3 + 4
= 80 + 10
= 90
(d) 19 + 17 + 13 + 14 + 21
= 19 + 21 + 17 + 3 + 11
= 40 + 20 + 11
= 71
(e) 33 + 24 + 13 + 14
= 30 + 3 + 20 + 4 + 10 + 3 + 14
= 60 + 10 + 14
= 84
(f) 28 + 23 + 9 + 22 = 50 + 22 + 1 + 9
= 50 + 22 + 10
= 82

9. (g) 29 + 23 + 28 + 16
= 29 + 1 + 20 + 2 + 28 +_16
= 30 + 30 + 36
= 96
(h) 27 + 4 + 29 + 35 = 27 + 3 + 1 + 29 + 35
= 30 + 30 + 35
= 95
4 (a) 7 = 2 + 5
(b) 12 = 5 + 7
(c) 18 = 5 + 13
18 = 7 + 11
(d) 36 = 13 + 23
36 = 17 + 19
36 = 29 + 7
(e) 42 = 19 + 23
42 = 29 + 13
(f) 48 = 19 + 29
5 (a) 10 = 2 + 3 + 5
(b) 23 = 3 + 7 + 13 = 5 + 7 + 11
(c) 38 = 2 + 7 + 29 = 2 + 13 + 23
(d) 37 = 3 + 5 + 29 = 3 + 11 + 23 or = 13 + 17 + 7
(e) 41 = 5 + 17 + 19 = 5 + 13 + 23 or = 5 + 7 + 29 = 7 + 11 + 23
(f) 49 = 3 + 17 + 29 = 7 + 13 + 29 or = 7 + 13 + 29 or = 7 + 19 + 23 = 13 + 17 + 19