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2.9: Estimate Products and Quotients of Fractions and Mixed Numbers

Difficulty Level: Basic / Basic Created by: CK-12
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Have you ever tried to estimate a product or a quotient? Take a look at this dilemma with fractions and mixed numbers.

4 \frac{1}{12} \times 12 \frac{3}{2}

To figure this out, you need to know how to estimate a product. You will know how to do this by the end of the Concept.

Guidance

Estimation is a useful strategy to use to check that your computation is reasonable. It is also a way to find an approximate answer to a solution.

To estimate products and quotients of mixed numbers, round the fractions to the nearest whole number. If the fraction is less than \frac{1}{2}, round down. If the fraction is greater than \frac{1}{2}, round up.

Estimate the product: 8 \frac{4}{11} \times 7\frac{11}{12}

Round the first number.

Since \frac{4}{11} is less than \frac{1}{2},8\frac{4}{11} rounds down to 8.

Round the second number.

Since \frac{11}{12} is greater than \frac{1}{2},7\frac{11}{12} rounds up to 8.

Now multiply to find the estimated product.

8\times8=64

A reasonable estimate is 64.

Here is another one.

Estimate the quotient: 22\frac{3}{10}\div 6\frac{9}{13}

Round the first number.

Since \frac{3}{10} is less than \frac{1}{2},22\frac{3}{10} rounds down to 22.

Round the second number.

Since \frac{9}{13} is greater than \frac{1}{2},6\frac{9}{13}rounds up to 7.

Now divide to find the estimated product. Since 22 is not divisible by 7, round it down to 21 to make compatible numbers that are easier to divide.

21\div 7=3

A good estimate for the quotient is 3.

Notice that you have to use some common sense and thinking to figure out that you had to round 22 down to 21 to find a good estimate.

Estimate each product or quotient.

Example A

6 \frac{1}{2} \times 4 \frac{1}{8}

Solution:7 \times 4 = 28

Example B

11 \frac{3}{4} \div 2 \frac{1}{10}

Solution:12 \div 2 = 6

Example C

\frac{3}{4} \times \frac{8}{9}

Solution:1 \times 1 = 1

Now let's go back to the dilemma from the beginning of the Concept.

4 \frac{1}{12} \times 12 \frac{3}{12}

First, round each value.

4 \frac{1}{12} becomes 4

12 \frac{3}{12} becomes 12

Now we can write a new problem.

4 \times 12 = 48

Our reasonable estimate is 48.

Vocabulary

Greatest Common Factor
a number that will divide evenly into both the numerator and the denominator of a fraction.
Product
the answer in a multiplication problem.
Quotient
the answer in a division problem.
Fraction
a part of a whole
Mixed Number
a number with a whole number and a fraction.
Improper Fraction
a number that is greater than a whole with a larger top number and a smaller bottom number.
Estimation
a reasonable answer

Guided Practice

Here is one for you to try on your own.

Estimate the following quotient.

14 \frac{11}{12} \div 2 \frac{7}{8}

Solution

Begin by rounding each value. Here is the new equation.

15 \div 3 = x

Now solve for x.

x = 5

This is our estimate.

Video Review

Khan Academy Reading Bar Graphs

Practice

Directions: Estimate each product or quotient.

1. \frac{7}{8} \times \frac{7}{8}

2. 3 \frac{1}{2} \times \frac{3}{4}

3. 6 \frac{2}{3} \times \frac{4}{5}

4. 8 \frac{1}{12} \times 3 \frac{1}{8}

5. 9 \frac{4}{5} \times 6 \frac{1}{9}

6. 12 \frac{1}{3} \times 4 \frac{5}{6}

7. 6 \frac{4}{7} \times 3 \frac{3}{8}

8. 12 \frac{1}{8} \div 3 \frac{1}{3}

9. 24 \frac{2}{10} \div 3 \frac{1}{3}

10. 28 \frac{1}{9} \div 7 \frac{1}{10}

11. 9 \frac{2}{3} \div 1 \frac{4}{5}

12. 14 \frac{1}{2} \div 3 \frac{1}{10}

13. 9 \frac{3}{10} \div 3 \frac{1}{9}

14. 16 \frac{4}{15} \div 2 \frac{1}{5}

15. 30 \frac{4}{12} \div 3 \frac{6}{18}

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Difficulty Level:

Basic

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Date Created:

Dec 19, 2012

Last Modified:

Mar 25, 2014
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