1. Knowing Our Numbers Worksheet With Answers Page 15
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25Example 24: Estimate each of the following using the general rule:
(a) 730 + 998
(b) 891 – 244
(NCERT)
(c) 12,780 + 2,888
(d) 28,292 – 21,496
(NCERT)
Solution:
(a) 730 + 998
Let’s round off to the nearest hundreds.
730 is rounded off to 700.
700
998 is rounded off to 1,000.
+ 1,000
Therefore, estimated sum of 730 and 998
1,700
= 700 + 1,000
= 1,700
(b) 891 – 244
Let’s round off to the nearest hundreds.
891 is rounded off to 900.
900
244 is rounded off to 200.
– 200
Therefore, estimated difference of 891 and 244
700
= 900 – 200
= 700
(c) 12,780 + 2,888
Let’s round off to the nearest thousands.
12,780 is rounded off to 13,000.
13,000
2,888 is rounded off to 3,000.
+ 3,000
Therefore, estimated sum of 12,780 and 2,888
16,000
= 13,000 + 3,000
= 16,000
(d) 28,292 – 21,496
Let’s round off to the nearest thousands.
28,292 is rounded off to 28,000.
28,000
21,496 is rounded off to 21,000.
– 21,000
Therefore, estimated difference of 28,292 and 21,496
7,000
= 28,000 – 21,000
= 7,000
Example 25: Give a rough estimate by rounding off to the nearest hundreds and also a closer
estimate by rounding off to the nearest tens:
(a) 439 + 334 + 4,317 (b) 3,25,215 – 25,370
(c) 4,89,348 – 48,365
(NCERT)
Solution:
(a) 439 + 334 + 4,317
On rounding off to the nearest hundreds:
439 is rounded off to 400.
400
334 is rounded off to 300.
300
4,317 is rounded off to 4,300.
+ 4,300
Therefore, estimated sum of 439 + 334 + 4,317
5,000
= 400 + 300 + 4,300
= 5,000
15
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