Page 43 - Revised Maths Wisdom Class - 3

Additi on of 4-Digit Numbers 41

Exercise 3E

Add the following.

(a) 82 + 10 (b) 137 + 10 (c) 331 + 100 (d) 417 + 400

(e) 2357 + 1000 (f) 3117 + 1000 (g) 3222 + 3000 (h) 6006 + 2000

Estimating the Sum

To quickly check the sum, we round off the numbers and add them. It can give us a
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rough estimate whether our answer is correct or not.

Let's Try

Example 1: Estimate the sum of 23 and 65 by rounding off the number to the nearest
tens. Estimated sum Actual sum

rounded to T O T O
Solution: 23 nearest tens 20 2 0 2 3

rounded to + 7 0 + 6 5
65 nearest tens 70 9 0 8 8

Thus, the estimated sum is nearer to the actual sum but not correct.

Example 2: Estimate the sum of 133 and 274 by rounding off the numbers to the nearest
hundreds. Estimated sum Actual sum
rounded to H T O H T O
Solution: 133 nearest hundreds 100 1 0 0 1
1
rounded to + 3 0 0 + 2 3 3
0
0
7
4
4
274 nearest hundreds 300 4 0 7
Thus, the estimated sum is nearer to the actual sum but not correct.
Example 3: Estimate the sum of 759 and 367 by rounding off the numbers to the nearest

hundreds.
Estimated sum Actual sum
rounded to H T O H T O
Solution: 759 nearest hundreds 800 8 0 0 7 5 9

rounded to + 4 0 0 + 3 6 7
367 nearest hundreds 400 12 0 0 11 2 6

Thus, the estimated sum is nearer to the actual sum but not correct.