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You are reading an older version of this FlexBook® textbook: CK-12 Middle School Math Concepts - Grade 8 Go to the latest version.

2.9: Estimate Products and Quotients of Fractions and Mixed Numbers

Difficulty Level: At Grade Created by: CK-12
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Practice Product Estimation with Mixed Numbers/Fractions
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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.

4112×1232

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 12, round down. If the fraction is greater than 12, round up.

Estimate the product: 8411×71112

Round the first number.

Since 411 is less than 12,8411 rounds down to 8.

Round the second number.

Since 1112 is greater than 12,71112 rounds up to 8.

Now multiply to find the estimated product.

8×8=64

A reasonable estimate is 64.

Here is another one.

Estimate the quotient: 22310÷6913

Round the first number.

Since 310 is less than 12,22310 rounds down to 22.

Round the second number.

Since 913 is greater than 12,6913rounds 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÷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

612×418

Solution:7×4=28

Example B

1134÷2110

Solution:12÷2=6

Example C

34×89

Solution:1×1=1

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

4112×12312

First, round each value.

4112 becomes 4

12312 becomes 12

Now we can write a new problem.

4×12=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.

141112÷278

Solution

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

15÷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. 78×78

2. 312×34

3. 623×45

4. 8112×318

5. 945×619

6. 1213×456

7. 647×338

8. 1218÷313

9. 24210÷313

10. 2819÷7110

11. 923÷145

12. 1412÷3110

13. 9310÷319

14. 16415÷215

15. 30412÷3618

Vocabulary

Estimation

Estimation

Estimation is the process of finding an approximate answer to a problem.
fraction

fraction

A fraction is a part of a whole. A fraction is written mathematically as one value on top of another, separated by a fraction bar. It is also called a rational number.
Greatest Common Factor

Greatest Common Factor

The greatest common factor of two numbers is the greatest number that both of the original numbers can be divided by evenly.
improper fraction

improper fraction

An improper fraction is a fraction in which the absolute value of the numerator is greater than the absolute value of the denominator.
Mixed Number

Mixed Number

A mixed number is a number made up of a whole number and a fraction, such as 4\frac{3}{5}.
Product

Product

The product is the result after two amounts have been multiplied.
Quotient

Quotient

The quotient is the result after two amounts have been divided.

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Difficulty Level:

At Grade

Grades:

Date Created:

Dec 19, 2012

Last Modified:

Nov 20, 2015
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