Page 73 - Start Up Mathematics_5

Addition and Subtraction of Fractions

We have already learnt how to add and subtract like and unlike fractions in the previous
class. Let’s quickly revise it through the given examples.

2
5
Example 12: Add and . Remember
9 9
To add or subtract like fractions,
5
Solution: 2 + = 2 + 5 = 7 simply add or subtract the
9 9 9 9 numerators and write the
Example 13: Add 13 and 8 . denominator below the sum.
20 15
Solution: LCM of 20 and 15 = 2 × 2 × 5 × 3 = 60 2 20 , 15

13 13 × 3 39 2 10 , 15
= =
20 20 × 3 60 5 5 , 15
8 8 × 4 32 3 1 , 3
= =
15 15 × 4 60 1 , 1

13 + 8 = 39 + 32 = 39 + 32 = 71 = 1 11 Remember
20 15 60 60 60 60 60
To add or subtract
unlike fractions,
Improper Mixed
fraction fraction convert them to like
fractions and then
Example 14: Subtract 7 from 13 . add or subtract them.
18 18
1
Solution: 13 – 7 = 13 – 7 = 6 = 2 × 3 = Lowest term
18 18 18 18 3 × 3 × 2 3

Example 15: Subtract 13 from 11 .
45 25
Solution: LCM of 25 and 45 = 5 × 5 × 3 × 3 = 225 5 25 , 45
11 11 × 9 99 5 5 , 9
= = 3 1 , 9
25 25 × 9 225
13 13 × 5 65 3 1 , 3
= = 1 , 1
45 45 × 5 225

11 – 13 = 99 – 65 = 34
25 45 225 225

EXERCISE 4.3

1. Add the following fractions. Reduce the sum to the lowest term (if possible).

(a) 41 and 15 (b) 64 and 31 (c) 15 and 11 (d) 34 and 11
53 53 125 125 21 42 16 20

(e) 19 and 8 (f) 12 and 9 (g) 8 and 12 (h) 13 and 21
22 33 18 24 5 25 22 32

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