VI. Add and Subtract Whole Numbers and Decimals
To add and subtract whole numbers and decimals, estimate or check
to make sure that your answer is reasonable.
- Add: 3,165,892 2,096,089
Use front digits to estimate the sum as
5,000,000. Align digits by place value.
The answer is close to the estimate.
3165892
2096089
5261981
1111
,,
,
,,
- Add: 5.0953 3.0107
Use front digits to estimate the sum as 8.
Align the digits by place value.
The answer is close to the estimate.
50953
30107
8106
1 1
- Subtract: 8,309,000 777,625
Align digits by place value. Subtract.
Add to check:
7,531,375 777,625 8,309,000 ✓
8309000
777 6 2 5
7531 375
72
12
10 8 10
9
10
9
10
,,
,
,,
- Subtract: 3 0.7185
Align digits by place value. Subtract.
Add to check:
2.2815 0.7185 3.0 ✓
3 0000 3 3.0000
07185
22815
210
9
10
9
10
9
10
8.1060 8.106
about
Skills Update 409
Practice Exercises
V.Estimate Sums and Differences
You can use rounding or front-end estimation to estimate
sums and differences.
- You can estimate a sum or difference by rounding:
Round each number to the greatest nonzero place of the least number.
Add or subtract the rounded numbers.
Add: Subtract:
6917
78
434
6920
80
430
7430 about
- 82
0.29
0.36
- 8
0.3
0.4
2.5
about
5931
723
5900
700
5200 about
0.087
0.058
0.09
0.06
0.03
Front-digit sum
Adjusted estimate
4164
987
3895
7000
2000
9000
1.82
0.29
0.36
1
1
2
about 9000
9561
742
0.47
0.13
about 0.3
- You can estimate a sum or difference using front-end estimation.
Add or subtract the front digits of the numbers with the greatest
place value. Write zeros for the other digits. Adjust the addition
estimate with the back digits.
