1. Fractions and Decimals
Lesson 8
Fractions and Decimals
Estimating Sums and Differences

2. Warm-up Round 542 to the nearest ten.
Round 1,389 to the nearest hundred.
Find the value of
Find the value of 23 – 15.

3. Estimating Sums and Differences
Target:
Estimate sums and differences of expressions with fractions and mixed numbers.

4. Estimating Sums or Differences Using Fractions
Round to 0, ½ or 1, whichever is closest.
If the numerator is very small compared to the denominator, estimate as 0.
If the numerator is about half of the denominator, estimate as ½.
If the numerator is nearly as big as the denominator, estimate as 1.
Add or subtract.

5. Example 1 Hayden had about of a box of pencils. Trevor had about
of a box. Kelsey had about of a box and Asha had
about of a box. About how many boxes of pencils do
they have altogether?
Add the estimated amounts.
They have about 2 boxes of pencils altogether.
Hayden
Trevor
Kelsey
Asha
The numerator is very small compared to the denominator.
The numerators are about half of their denominators.
The numerator is nearly as big as the denominator.

6. Example 2 Asha Found that instead of of a box of pencils, she had
of a box. About how much less does she have than she
originally thought?
Write the problem.
Round to 0, or 1.
Subtract.
Asha has about half a box less than she thought she had.

7. Estimating Sums or Differences Using Mixed Numbers
Round to the nearest whole number.
Add or subtract.

8. Example 3 Estimate the value of . Write the problem.
Round to the nearest whole number.
Add.

9. Example 4 According to the Guinness Book of World Records, the
world’s tallest man, Robert Pershing Wadlow, was
feet tall. The world’s shortest woman, Zhu Haizhen, was
feet tall. Approximately how much taller was the
tallest man than the shortest woman?
Write the problem.
Round.
Subtract.

10. Exit Problems
Estimate the value of each expression.

11. Communication Prompt
What are some situations where estimating with fractions or mixed numbers would be useful?