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Mixed Number and Fraction Estimation

Estimating sums and differences

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Mixed Number and Fraction Estimation
License: CC BY-NC 3.0

Travis was practicing for the long jump. His first jump was 834 feet. After practicing for a month, he was able to add 213 feet to his record. About how many feet is Travis able to jump? Estimate the distance. 

In this concept, you will learn how to estimate the sums and differences of fractions and mixed numbers.

Estimating Mixed Numbers and Fractions

A sum is the answer in addition problem. You can also estimate the sum of fractions. To estimate a sum of two fractions, round the fractions to the nearest half. Here is an addition problem.

38+17=

First, round each fraction to the nearest half.

Let’s start with 38. For a whole divided into 8 parts, 12=48. 38 is rounded to 12.

For a whole divided into 7 parts, one-half is between 37 and 4717 is rounded 0. 

3812120Then, rewrite the problem and find the sum.

12+0=12

The estimate sum is 12.

When estimating the sum of mixed numbers, round to the nearest whole number instead of the nearest half. Here is an addition problem involving mixed numbers. 

345+219=

First, round each mixed number to the nearest whole number.

 345  will either round down to 3 or up to 4. Look at the fraction part of the mixed number. 45 is greater than 12. Round up to 4.

219  will either round down to 2 or up to 3. One-ninth is a very small fraction and less than 12. Round down to 2. 

34521942 

Then, rewrite the problem and find the sum.

4+2=6

The estimate sum is 6.

When talking about a difference, you are talking about subtraction. Estimating the difference of fractions and mixed numbers is similar to estimating sums. Round each fraction or mixed number and then subtract to find the estimate.

4537=

First, round each fraction to the nearest half. 

For a whole divided into 5 parts, one-half is between 25 and 3545 is rounded to 1. 

For a whole divided into 7 parts, is one-half is between 37 and 47.  37 is rounded to 12.

4537112

Then, rewrite the problem and subtract.

112=12

The estimate difference is 12.

Examples

Example 1

Earlier, you were given a problem about Travis practicing the long jump.

Travis started at 834 feet and was able to add 213 feet to his long jump record. Round the numbers and add the numbers to find an estimate of his current long jump record. 

 834+213

First, round the mixed numbers to the nearest whole number. 

 83492132

Then, rewrite the problem and add.

 9+2=11

Travis can now jump approximately 11 feet.

Example 2

Estimate the difference:

634218=.

First, round each mixed number to the nearest whole number. Look at the fraction part of each mixed number. 

34 is greater than 12. 634 rounds up to 7.

18 is less than 12. 218 rounds down to 2.

Then, rewrite the problem and subtract.

72=5

The estimate sum is 5.

Example 3

Estimate the sum: 49+78=.

First, round each fraction to the nearest half.

 4978121

Then, rewrite the problem and add.

 12+1=112

The estimate sum is 112.

Example 4

Estimate the sum: 67+111=.

First, round each fraction to the nearest half.

\begin{align*}\frac{6}{7} & \approx 1 \\ \frac{1}{11} & \approx 0\end{align*}

Then, rewrite the problem and add.

 \begin{align*}1+0=1\end{align*}

The estimate sum is \begin{align*}1\end{align*}.

Example 5

Estimate the difference: \begin{align*}5 \frac{1}{3} - 2 \frac{3}{4} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}.

First, round the mixed numbers to the nearest whole number.

 \begin{align*}5 \frac{1}{3} & \approx 5 \\ 2 \frac{3}{4} & \approx 3\end{align*}

Then, rewrite the problem and find the difference.

 \begin{align*}5-3=2\end{align*}

The estimate difference is \begin{align*}2\end{align*}.

Review

Estimate the following sums.

  1. \begin{align*}\frac{1}{5} + \frac{4}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  2. \begin{align*}\frac{8}{9} + \frac{4}{6} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  3. \begin{align*}\frac{2}{9} + \frac{4}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  4. \begin{align*}\frac{3}{6} + \frac{2}{3} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  5. \begin{align*}\frac{5}{6} + \frac{2}{3} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  6. \begin{align*}\frac{1}{12} + \frac{9}{11} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  7. \begin{align*}\frac{6}{12} + \frac{10}{11} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  8. \begin{align*}1 \frac{1}{10} + 2 \frac{1}{2} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  9. \begin{align*}4 \frac{2}{3} + 5 \frac{4}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  10. \begin{align*}7 \frac{1}{9} + 8 \frac{1}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  11. \begin{align*}14 \frac{5}{9} + 8 \frac{4}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  12. \begin{align*}4 \frac{2}{3} + 7 \frac{1}{7} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  13. \begin{align*}18 \frac{1}{13} + 7 \frac{2}{10} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  14. \begin{align*}11 \frac{12}{13} + 4 \frac{1}{10} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  15. \begin{align*}22 \frac{5}{7} + 11 \frac{1}{5} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}

Estimate each difference.

  1. \begin{align*}\frac{4}{5} - \frac{1}{4} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  2. \begin{align*}\frac{4}{5} - \frac{3}{4} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  3. \begin{align*}\frac{9}{10} - \frac{3}{6} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  4. \begin{align*}\frac{11}{12} - \frac{1}{7} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}
  5. \begin{align*}\frac{10}{13} - \frac{1}{10} = \underline{\;\;\;\;\;\;\;\;\;}\end{align*}

Review (Answers)

To see the Review answers, open this PDF file and look for section 6.3. 

Resources

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Vocabulary

TermDefinition
Difference The result of a subtraction operation is called a difference.
Estimate To estimate is to find an approximate answer that is reasonable or makes sense given the problem.
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.
Mixed Number A mixed number is a number made up of a whole number and a fraction, such as 4\frac{3}{5}.
Sum The sum is the result after two or more amounts have been added together.

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