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In this 5th grade lesson, I explain how to simplify fractions before multiplying them. This is an extremely useful technique. It makes the fraction multiplication much easier because the numbers to be multiplied are smaller after the simplification.
1. Simplify the fractions. Write the simplified numerator and denominator above and below the old ones.
and a tiny “2” below the “6”. In the other example, 4/10 is simplified to 2/5 before multiplying. Why does this work?Obviously, we can write1/2 instead of 3/6, or 2/5 instead of 4/10, since they are equivalent.2. Simplify one or both fractions before multiplying. Use equivalent fractions. Look at the example.
3. Simplify “criss-cross” before you multiply.
4. Simplify before you multiply.
1) Think of the fraction line as division. The problem is therefore the same as 27 ÷ 45 × 45.
5. Simplify and multiply.
6.A toy block is 3/8 in. tall. How tall is a stack of 8 of them?
7. Sandra buys 3/4 kg of meat every week. How much meat does she buy in a year? 8. The morning after his birthday, there is 12/20 of Sam's birthday cake left. He eats 2/3 of what is left.
9.Multiply three fractions. Simplify before multiplying.
10. a. Draw a bar model for this situation. Matthew pays 1/5 of his salary in taxes. b. Suppose Matthew’s salary is $2,450.
This lesson is taken from Maria Miller's book Math Mammoth Fractions 2, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller. Math Mammoth Fractions 2A self-teaching worktext that teaches fractions using visual models, a sequel to Math Mammoth Fractions 1. The book covers simplifying fractions, multiplication and division of fractions and mixed numbers, converting fractions to decimals, and ratios. Download ($5.75). Also available as a printed copy. Math Lessons menu
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