6th Grade Math Textbook, Progress

Estimate Decimal Sums and Differences

1-6

 1 .82


 0 .29


 0 .36

1

1


1. 82 
1.8


0. 29 
0.3


0. 36 
0.4

2.5

1. 82


0. 29


0.36

Adjusted estimate: 1 
 1  2

about 1

You can use front-end estimation or

rounding to estimate decimal sums.

Estimate: 1.82
0.29
0.36

To use front-end estimation:

Add the front digits.

Adjust the estimate by using

the remaining digits to make 1.

The estimated sum is 2.

To use roundingto estimate:

Round each decimal to the greatest

nonzeroplace of the least number.

Add the rounded numbers.

Both 2 and 2.5 are reasonable estimates of the actual sum of 2.47.

Use the same two methods to estimate differences of decimals.

Front-end Estimation Rounding

Subtract the front digits. 
Round to the greatest nonzero


 
place of the lesser number.

Write zeros for the other digits in the 
Subtract the rounded numbers.


whole-number part of the number.

 9 3.36  9 3.36 
 90

 4 5.09  4 5.09  50

about 50.00 about 40

Both 50 and 40 are reasonable estimates of the actual difference of 48.27.

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