Page 56 - Start Up Mathematics_3

Th H T O Th H T O Th H T O
(d) (e) (f)
? 9 2 0 7 3 ? 4 ? 9 0 4

– 3 ? 5 ? – 2 ? 5 1 – 1 2 ? 3

3 4 ? 4 ? 4 3 ? 5 ? 3 1

4. Fill in the blanks.

(a) 1212 – 0 = __________ (b) 4799 – 1 = __________

(c) 8088 – 8088 = __________ (d) 9999 – 1 = __________

Estimating Differences

To estimate the difference, round off the minuend and subtrahend to the nearest
10, 100, 1000 and subtract.

Example 9: Find the difference between 6875 and 3256 using estimation to the
nearest 100 and compare with the actual value.

Solution: Actual Value Estimated Value
Th H T O Th H T O

6 8 6 7 15 5 6 9 0 0 (6875 is rounded
off to 6900)
– 3 2 5 6 – 3 3 0 0
(3256 is rounded
3 6 1 9 3 6 0 0 off to 3300)

The actual value 3619 when rounded off to the nearest 100 is 3600.

So, the estimated value is correct.

Example 10: Find the difference between 6923 and 4549 using estimation to the
nearest 10 and compare with the actual value.

Solution: Actual Value Estimated Value

Th H T O Th H T O

8 1 11 13 6 8 9 12 2 0 (6923 is rounded
6 9 2 3 off to 6920)
– 4 5 5 0
– 4 5 4 9 (4549 is rounded
2 3 7 0
2 3 7 4 off to 4550)

The actual value 2374 when rounded off to the nearest 10 is 2370. So,
the estimated value is correct.

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