Page 14 - Maths Class 06

Estimation
Numbers are very often used in our day-to-day life. Usually we need to speak of exact number or things,
but at times, only an estimate of the same is sufficient and even preferred.
Take, for instance, the following two news items:

1. Approx. 30,000 people were killed and more than 20,000 injured in the recent earth quake.
2. Approx. 15 million passengers are carried over 63,000 km route of railway track every day.

We know that the numbers quoted in the news items are not exact counts, but are estimates an give an
idea of the quantity.

To estimate a quantity, we use the process of rounding off

How to Round off a Number?

1. Round off 67 to the near est ten.
67

40 50 60 70 80 90 100
67 ¾® 70
67 is closer to 70 than to 60. So, 67 is rounded off upwards to 70.

2. Round off 92 to the near est ten.
92

40 50 60 70 80 90 100
92 ¾® 90

92 is closer to 90 than to 100. So, 92 is rounded off downwards to 90.
3. Round off 45 to the near est ten.
45

40 50 60 70 80 90 100
45 ¾® 50
45 is halfway between 40 and 50. So, 45 is rounded off upwards to 50.
Remember, when a number is halfway. It is a convention to round it up.

4. Round off 167 to the nearest ten.

167

120 130 140 150 160 170 180
167 ¾® 170
167 is closer to 170 than to 160. So, 167 is rounded off upwards to 170.

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