Page 103 - Start Up Mathematics_5

7

Decimals—Four Operations

We already know that the four basic mathematical operations are addition, subtraction,
multiplication and division. In this lesson, we will learn to add, subtract, multiply and divide
decimal numbers.

Addition and Subtraction

Let’s understand addition and subtraction of decimal numbers with the help of pictures.

0.2 + 0.6 = 0.8 0.9 – 0.2 = 0.7

Addition and subtraction of decimal numbers is done in the same way as for whole numbers.
We first change the unlike decimals to like decimals. Then place decimal points one below
the other, write the numbers to be added or subtracted and finally proceed.

Example 1: Add 461.24 and 38.05. Example 2: Add 24.076, 89.5 and 7.12.

2
Solution: 4 6 1 . 2 4 Solution: 2 4 . 0 7 6
+ 3 8 . 0 5 8 9 . 5 0 0
4 9 9 . 2 9 + 7 . 1 2 0

1 2 0 . 6 9 6

Example 3: Subtract 49.72 from 82.01.

11 9 Remember
7 1 10 11
Solution: 8 2 . 0 1
– 4 9 . 7 2 • We can add decimal numbers
in any order. The sum will
3 2 . 2 9 remain the same.
• If a decimal number is
Example 4: Simplify 71.124 + 25.06 – 39.74. subtracted from itself, the
difference is zero.
15
8 5 11
Solution: 7 1 . 1 2 4 9 6 . 1 8 4
+ 2 5 . 0 6 0 – 3 9 . 7 4 0
9 6 . 1 8 4 5 6 . 4 4 4

So, 71.124 + 25.06 – 39.74 = 56.444

95