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eStimating difference

Like addition, we can also estimate the difference by rounding off.
Example 1: Estimate the difference of 64 and 87 by rounding them to the nearest 10.

Then, compare it with their actual difference.

Solution: Actual difference Estimated difference
t O t O

8 7 rounded up 9 0
– 6 4 rounded down – 6 0
2 3 3 0

The estimated difference is greater than the actual one.
Example 2: A shopkeeper had 662 balls. He sold 245 balls. Estimate the number of unsold

balls by rounding off to the nearest 10. Is the number of balls left unsold more than or
less than 400?
Solution: Actual difference Estimated difference

H t O H t O
6 6 2 rounded down 6 6 0
– 2 4 5 rounded up – 2 5 0
4 1 7 4 1 0

The estimated number of unsold balls is 410.
Clearly, the shopkeeper has more than 400 balls left unsold with him.

Practice time 3d

Find the estimated difference by rounding to the nearest 10. Also, find the actual
difference and compare.

1. Actual difference Estimated difference 2. Actual difference Estimated difference

t O t O t O t O
8 7 round off 9 4 round off
– 2 3 round off – – 6 5 round off –

3. Actual difference Estimated difference 4. Actual difference Estimated difference

H t O H t O H t O H t O

1 6 7 round off 2 6 4 round off
– 9 4 round off – – 1 8 5 round off –

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