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

Problem 2:
Calculate tex2html_wrap_inline56 and reduce your answer.
The answer is tex2html_wrap_inline58 .
The denominators are different, so you must build each fraction to a form where they both have the same denominator. Since 5 divides into 15 evenly, you only have to build the fraction tex2html_wrap_inline60 to an equivalent fraction with a denominator of 15. tex2html_wrap_inline62.
tex2html_wrap_inline56 can now be written tex2html_wrap_inline66.
Combine the numerators for the numerator in the answer:

4 - 9 = -5.
The answer is tex2html_wrap_inline72 .
This fraction now needs to be reduced. tex2html_wrap_inline74

Now prove to yourself with your calculator that your answer is correct. Calculate 4 divided by 15, calculate 3 divided by 5, and combine the results. Now divide -1 by 3. Both answers should be the same. If you are correct, the answers are the same (equivalent) and you have successfully combine two fractions using subtraction.

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