Page 40 - Maths Skill - 3
P. 40
38 Maths
Let’s Attempt
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
+ 7 0 + 6 5
rounded to 9 0 8 8
65 nearest tens 70
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
Solution: 133 nearest hundreds 100 H T O H T O
1 0 0 1
+ 3 0 0 1 3 3
rounded to + 2 7 4
274 nearest hundreds 300 4 0 0 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
Solution: 759 nearest hundreds 800 H T O H T O
0
8
0
9
5
7
+ 4 0 0 + 3 6 7
rounded to 12 0 0 11 2 6
367 nearest hundreds 400
Thus, the estimated sum is nearer to the actual sum but not correct.
Exercise 3.9
1. Estimate the sum by rounding off the numbers to the nearest tens. Also, find the
actual sum.
(a) 65 + 24 (b) 46 + 33 (c) 55 + 31 (d) 73 + 18
2. Estimate the sum by rounding off the numbers to the nearest hundreds. Also, find
the actual sum.
(a) 143 + 265 (b) 267 + 324 (c) 343 + 575 (d) 525 + 268