If you are interested in knowing how to estimate a sum, this article will give you clear information on estimating the sum. It includes the basic knowledge for estimating a sum, how to estimate a sum. You can also find the step-by-step procedures for estimating the sum of two-digit numbers, estimating the sum of three-digit numbers. Furthermore, check out the Solved Examples and understand how do you use rounding when estimating a sum.
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Estimating a Sum – Definition
The estimation of a sum is close to the answer of an original sum, but not exact. For example 29+12=41. The estimated sum of 29,12 is 30+10=40
How to Estimate a Sum?
It is an easy method to estimate the sum of two numbers. Estimating a sum of numbers includes two steps. They are as follows
- Estimate a sum of two numbers by rounding. i.e. addends are rounded.
- Then add the rounded numbers.
How to Estimate the Sum of Two-Digit Numbers?
In the two-digit numbers, we have to round the number to the nearest tens place i.e. only one place estimate. For estimating the nearest 10, we see the digit at one’s place. It is converted to 0 or 10 as per the digit. If the digit is < 5, it is converted to zero and if it is > 5, it is converted to10.
Examples on Estimating a Sum of Two Digit Numbers
 Example 1:
Estimate the sum of 38,12 i.e. 38 + 12?
Solution:
1. We have to round the numbers to the nearest 10.
38 → 40
12 → 10
38 is nearest to 40
12 is nearest to 10
2. Add the rounded numbers.
40 + 10 = 50
Therefore the estimated sum of 38, 12 is 50.
Example 2:
Estimate the sum of 55,13 i.e. 55 + 13?
Solution:
1. We have to round the number to the nearest 10.
55 → 60
13 → 10
55 is nearest to 60.
13 is nearest to 10.
2. Add the rounded numbers.
60+10=70
Therefore, the estimated sum of 55,13 is 70.
Example 3:
Estimate the sum of 62, 28?
Solution:
1. First, we have to round the numbers to the nearest 10.
62 → 60
28 → 30
so 62 is nearest to 60
28 is nearest to 30.
2. Add the rounded numbers.
60+30=90
Therefore the estimated sum of 62, 28 is 90.
Example 4:
Estimate the sum of 57, 78?
Solution:
1.First, we have to round the numbers to the nearest 10.
57 → 60
78 → 80
so 57 is nearest to 60
78 is nearest to 80.
2. Add the rounded numbers.
60+80=140
Therefore the estimated sum of 57, 78 is 140.
Example 5:
Estimate the sum of 45, 63?
Solution:
1. We have to round the number to the nearest 10.
45 → 50
63 → 60
45 is nearest to 50.
63 is nearest to 60.
2. Add the rounded numbers.
50+60=110
Therefore, the estimated sum of 45,63 is 110.
How to Estimate a Sum of Three-Digit Numbers?
In the three-digit numbers also, first, we have to round the number to the nearest tens place i.e. only one place estimate. To estimate to the nearest 10, we see the digit at one’s place. It is converted to 0 or 10 as per the digit. If the digit is < 5, it is converted to zero and if the digit is > 5, it is converted to 10.
Estimating the Sum of Three-Digit Numbers Examples
Example 1:
Find the estimated sum of three-digit numbers 396, 110?
Solution:
1. We have to round the number to the nearest 10.
396 → 400
110 → 100
396 is nearest to 400.
110 is nearest to 100.
2. Add the rounded numbers.
400+100=500
Therefore, the estimated sum of 396,110 is 500.
Example 2:
Find the estimated sum of three-digit numbers 488, 108, and also the actual sum?
Solution:
1. We have to round the number to the nearest 10.
488 → 500
108 → 100
488 is nearest to 500.
108 is nearest to 100.
2. Add the rounded numbers.
500+100=600
Therefore, the estimated sum of 488,108 is 600.
Actual sum of 488,108 is488+108 =596.
Example 3:
Find the estimated sum of three-digit numbers 623, 568?
Solution:
1. We have to round the number to the nearest 10.
623 → 600
568 → 600
623 is nearest to 600.
568 is nearest to 600.
2. Add the rounded numbers.
600+600=1200
Therefore, the estimated sum of 623,568 is 1200.
Example 4:
Find the estimated sum of three-digit numbers 123, 848?
Solution:
1. We have to round the number to the nearest 10.
123 → 100
848 → 900
123 is nearest to 100.
848 is nearest to 900.
2. Add the rounded numbers.
100+900=1000
Therefore, the estimated sum of 123,848 is 1000.
Example 5:
Find the estimated sum of three-digit numbers 387,115?
Solution:
1. We have to round the number to the nearest 10.
387 → 400
115 → 100
387 is nearest to 400.
115 is nearest to 100.
2. Add the rounded numbers.
400+100=500
Therefore, the estimated sum of 387,115 is 500.