Page 54 - Start Up Mathematics_4

(c) TTh Th H T O (d) L TTh Th H T O

7 6 4 0 3 9 1 5 0 8 4
– ? 8 ? 1 6 – ? 6 ? 4 2 ?

3 ? 8 ? ? 3 ? 0 ? ? 7

Estimating Differences

To estimate the difference, round off the minuend and subtrahend to the nearest 10, 100,
1,000, 10,000 and so on and then subtract the rounded off numbers.

Example 14: Estimate the difference between 58,234 and 35,794 by rounding off the
numbers to the nearest 100. Check whether the estimated difference is correct
or not.

Solution: Estimated Value Actual Value

TTh Th H T O TTh Th H T O

7 12 11
5 8 2 0 0 7 1 13
5 8 2 3 4
– 3 5 8 0 0 – 3 5 7 9 4
2 2 4 0 0
2 2 4 4 0

The actual value 22,440 when rounded off to the nearest 100 is 22,400. So,
the estimated value is correct.

Example 15: Estimate the difference between 7,45,236 and 4,63,815 by rounding off the
numbers to the nearest 1,000. Check whether the estimated difference is
correct or not.
Solution: Estimated Value Actual Value

L TTh Th H T O L TTh Th H T O
6 14 6 14 4 12
7 4 5 0 0 0 7 4 5 2 3 6

– 4 6 4 0 0 0 – 4 6 3 8 1 5

2 8 1 0 0 0 2 8 1 4 2 1

The actual value 2,81,421 when rounded off to the nearest 1,000 is 2,81,000.
So, the estimated value is correct.

Solving Word Problems
Example 16: Tarun and Ravi have 21,618 coins. If Tarun has 15,025 coins, how many coins
does Ravi have?

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