6th Grade Math Textbook, Fundamentals

Lesson 4-4 for exercise sets. &KDSWHU 

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Estimate the sum or difference by rounding each number to the nearest tenth.

1.410.3 18.01 2.17.6 2.98 3.0.87 0.44 4.7.3026 45.217 0.746

Estimate the sum or difference by using front-end estimation.

5.8.132 7.0802 6.9.2 3.7 7. 2.0775 (1.03391) (2.605)

Estimate the sum by using clustering.

8.5.32 4.98 5.01 9.8.06 7.77 8.45 7. 9 10. 12.986 13.003 13.299 13.196

11.Discuss and Write Explain the steps you used to find the answer to exercise 3 above.

Key Concept

Front-End Estimation with Decimals

• To estimate the sum or difference, add or subtract the front digits in each number.


• For addition only, adjust the estimate, using the digits in the next place to the right.

Estimate the sum:

5.863 1.185 6.51 0.007 4.39

5.863

1.1 85

6.51

0.0 07

4.39

16

Estimate: 16 1  1  18

0.5 0.3 is about 1.

0.8 0.1 is about 1.

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Estimate the difference:

9.482 4.189

9.482

4.189

5

Estimate: 9 4  5

Method 2 Round to the Nearest Hundredth

589.483 3 5, so 8 stays as 8 hundredths.

24.678 8 5, so 7 rounds to 8 hundredths.

589.483 589.48

24.678  24.68

564.80

So, when each addend is rounded to the nearest hundredth,

589.483 24.678 564.80.

When rounding decimals, drop

all digits to the right of the digit

being rounded.

You can use front-end estimation to estimate sums and differences of decimals

when the front-end digits of all the numbers have the same place value.

You can also estimate by “clustering.” When several addends are close

to a certain value, multiply that value by the number of addends.

Estimate by clustering: 9.32 8.7 9.13 All 3 numbers cluster around, or are close to, 9.

So 9.32 8.7 9.13 is about 3 • 9, or 27.