**Rule 19:**- To subtract, the denominators must be equal. You
essentially following the same steps as in addition.
**1.**- Build each fraction so that both denominators are equal.
**2.**- Combine the numerators according to the operation of subtraction or additions.
**3.**- The denominators will be the denominator of the built-up fractions.
**4.**- Reduce the answer.

**Problem 4:**- Calculate and reduce your answer.
**Answer:**- The answer is .
**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)

Combine the numerators: 80 - 63 = 17.

The answer is .

This answer is already reduced so you can skip step 4.

**Check:**- You can check the answer with your calculator. Calculate 10
divided by 21, 9 divided by 24, and combine the answers. Now divide 17 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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