Page 23 - Start Up Mathematics_6

(b) 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
(c) 28,292 – 21,496
Let’s round off to the nearest thousands.
28,292 is rounded off to 28,000.
21,496 is rounded off to 21,000.
Therefore, estimated difference of 28,292 and 21,496 28,000
= 28,000 – 21,000 – 21,000
7,000
= 7,000
Example 23: 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.
334 is rounded off to 300.
4,317 is rounded off to 4,300.

Therefore, estimated sum of 439 + 334 + 4,317 400
= 400 + 300 + 4,300 300
= 5,000 + 4,300
On rounding off to the nearest tens: 5,000
439 is rounded off to 440.
334 is rounded off to 330.
4,317 is rounded off to 4,320.
Therefore, estimated sum of 439 + 334 + 4,317 440

= 440 + 330 + 4,320 330
= 5,090 + 4,320
(b) 3,25,215 – 25,370 5,090
On rounding off to the nearest hundreds:
3,25,215 is rounded off to 3,25,200.
25,370 is rounded off to 25,400.

Therefore, estimated difference of 3,25,215 – 25,370 3,25,200
= 3,25,200 – 25,400 – 25,400
2,99,800
= 2,99,800
On rounding off to the nearest tens:
3,25,215 is rounded off to 3,25,220.

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