Rule 18:
To add fractions, the denominators must be equal. Complete the following steps to add two fractions.
1.
Build each fraction so that both denominators are equal.
2.
Add the numerators of the fractions.
3.
The denominators will be the denominator of the built-up fractions.
4.

Problem 4:

Solution:
The denominators are different; therefore, the first step is to build the fractions to fractions with common denominators. 21 can be factored as follows: 21 = 3 7 and 24 can be factored as follows: 24 = 3 8.

Rewrite both fractions where the denominators are in factored form.

.

Multiply each fraction by the form of 1 that will yield denominators with the same set of factors. (i.e., you can find each set of factors in the denominator of the answer)

80 + 63 = 143.

Check:
You can check the answer with your calculator. Calculate 10 divided by 21, 9 divided by 24, and add the answers. Now divide 143 by 168. Both answers should be the same. If you are correct, the answers are the same (equivalent) and you have successfully added two fractions.

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