Basic Algebra and Geometry Made a Bit Easier Lesson Plans:
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Lesson 72: Multiplying Fractions
In this quick and easy lesson, we'll learn how to multiply fractions.
First, review all of the previous lessons on fractions. Make sure that you fully understand them. To multiply fractions, they do not have to have a common denominator like they did when adding and subtracting. All we have to do to multiply fractions is multiply the numerators, and then multiply the denominators. Sometimes people refer to this as "multiplying across." Memorize this procedure.
For example, to multiply 2/3 x 3/5, we multiply the numerators to
get 6, and the denominators to get 15. The answer is 6/15.
Let's try another. We'll multiply 4/5 x 5/6, and get 20/30.
We would probably want to reduce our answer to lowest terms by
dividing numerator and denominator by 10. See previous lessons
for more about this, including the lesson on
GCF. We look for the GCF of the numerator and denominator,
and that is what we should divide by. In this case, the
fraction is reduced to 2/3.
To multiply a fraction times a whole number, all we have to do is put the whole number of a denominator of 1, which doesn't change it. Then we can easily multiply. For example, to multiply 2/9 x 4, we'll convert 4 into 4/1. Now we can multiply and get 8/9.
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