Lesson 3, Topic 1
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# Sum & Difference

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### Sum:

The sum of two or more numbers is the result obtained when they are added together.

For example: The sum of 18, 22, and 160 is

18 + 22 + 160 =  200

### Difference:

The difference between two numbers is the result obtained when one of the numbers is subtracted from the other.

Positive difference: Larger number – Smaller No

Negative difference: Smaller No â€“ Larger No

### Example 1

Find the sum of the following

a. 89 and 98
b. -75 and 105
c. -6.8 and -7.5
d. -7, -89 and 56

Solution

a. 89 and 98 = 187

b. -75 and 105 = 105 -75 = 30

c. -6.8 and -7.5

= -6.8 – 7.5 = -14.3

d. -7, -89 and 56

56 â€“ 7 â€“ 89

56 â€“ 96 = -40

### Example 2

Add 15.5Â  to the positive difference betweenÂ 43.6 and 27.8

Solution

### Example 3

Add 18 to the negative difference between 56 and 45

Solution

45 – 56 =  -11

18 + – 11

=  18 – 11

= 7

### Example 4

From the sum of 78 and 129 subtract 264Â

Solution

### Example 5

The sum of a certain number and 18 is 40.  Find the number.

Solution

LetÂ the certain number be x

x + 18 = 40

= 40 – 18

= 22

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