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Approximation and Estimation

Rounding off Numbers

To ’round off’ or ‘approximate’ a number to a desired degree of accuracy, we-

a. round the number up if the next digit is 5 or more

b. round the number down if the next digit is less than 5.

We represent approximately equal to as and approximately as ‘~’


1. 73 is close to 70 if approximating to or rounding in “tens”. So

73 ~ 70 (Read as 73 is approximately equal to 70)

2. 86 is close to 90 when rounded off to the nearest “tens”, or approximate to the nearest “tens”

86 ~ 90

3. 650 ~ 700 when rounded off to the nearest hundreds

4. 26432 rounded off to

a. nearest 100 is 264 / 32  ~  26400

b. nearest 10,000 is 2 / 6432  ~  30000

Strategy to Round off Numbers

1. Put a line where you want to round off. In the above example 3 to round off 650, put a big line after 6, because 6 is in the hundreds place and you want to round to the nearest hundred.


2. The digit before the big line (6 in this case) will go up by 1, and the rest of the digits after the line will become 0, since the number after the line is 5. So the answer is 700…

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