Page 26 - Start Up Mathematics_6

On rounding off 8,024 to its nearest thousands, it becomes 8,000.
Therefore, estimation is reasonable.

Example 26: Estimate and compare with the actual difference:
(a) 1,355 – 566 (b) 67,983 – 23,865
Solution: (a) 1,355 – 566
Let’s round off to the nearest hundreds.
1,355 is rounded off to 1,400.
1,400
566 is rounded off to 600. – 600
Therefore, estimated difference = 1,400 – 600 800
= 800
However, actual difference = 1,355 – 566 1,355
= 789 – 566
On rounding off 789 to its nearest hundreds, it becomes 800. 789
Therefore, estimation is quite reasonable.
(b) 67,983 – 23,865

Let’s round off to the nearest thousands.
67,983 is rounded off to 68,000.
23,865 is rounded off to 24,000. 68,000
Therefore, estimated difference = 68,000 – 24,000 – 24,000
44,000
= 44,000
However, actual difference = 67,983 – 23,865
= 44,118 67,983
On rounding off 44,118 to its nearest thousands, it – 23,865
becomes 44,000. 44,118
Therefore, estimation is quite reasonable.
Example 27: Estimate each of the following products by rounding off each number to its nearest
hundreds:
(a) 377 × 432 (b) 245 × 598

Solution: (a) 377 × 432
Rounding off each number to the nearest hundreds:
377 is rounded off to 400.

432 is rounded off to 400.
Therefore, estimated product = 400 × 400
= 1,60,000
(b) 245 × 598

Rounding off each number to the nearest hundreds:
245 is rounded off to 200.
598 is rounded off to 600.

Therefore, estimated product = 200 × 600
= 1,20,000

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