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Subject – Mathematics

Chapter 4 – FRACTIONS

Sub-topic-7:- ADDITION AND SUBTRACTION OF UNLIKE FRACTION
AND WORD PROBLEMS

In addition and subtraction of unlike fractions, we first convert them into corresponding
equivalent like fractions and then they are added or subtracted.

Following steps are used to do the same.

Step I:

Obtain the fractions and their denominators.

Step II:

Find the LCM (least common multiple) of the denominators.

Step III:

Convert each fraction into an equivalent fraction having its denominator equal
to the LCM (least common multiple) obtained in Step II.

Step IV:

Add or subtract like fractions obtained in Step III.

For Example:

1. Add ²/₃ and ³/₇.

Solution:

The LCM (least common multiple) of the denominators 3 and 7 is 21.

So, we convert the given fractions into equivalent fractions with denominator
21.

We have,
2 3
/ 3 + / 7

= (2 × 7) / (3 × 7) + (3 × 3) / (7 × 3)

[since 21 ÷ 3 = 7 and 21 ÷ 7 = 3]