How to round numbers?

Irina Belova
Irina Belova
July 30, 2014
How to round numbers?

Rounding numbers is the simplest mathematical operation. To be able to correctly round the numbers, you need to know three rules.

Rule 1

When we round a number to a certain digit, we must get rid of all the digits to the right of this digit.

For example, we need to round the number 7531 to hundreds. This number is five hundred. To the right of this digit are the numbers 3 and 1. Turn them into zeros and get the number 7500. That is, rounding the number 7531 to hundreds, we got 7500.

When rounding off fractional numbers, everything happens the same way, only extra digits can be simply discarded. Suppose we need to round the number 12.325 to the tenth. To do this, after the comma, we must leave one number - 3, and all the numbers on the right, we discard. The result of rounding the number 12.325 to tenths is 12.3.

Rule 2

If to the right of the left digit, the discarded digit is 0, 1, 2, 3, or 4, then the digit we leave does not change.

This rule worked in the two previous examples.

So, when rounding the number 7531 to hundreds of the closest ones, three were rejected. Therefore, the number we left, - 5 - has not changed.The result of rounding was the number 7500.

In the same way, when rounding the number 12,325 to the tenth digit, which we dropped after the three, there was a two. Therefore, the rightmost of the left numbers (three) when rounding has not changed. It turned out 12.3.

Rule 3

If the leftmost of the dropped numbers is 5, 6, 7, 8, or 9, then the rank to which we round is increased by one.

For example, you need to round the number 156 to dozens. This number is 5 dozen. In the discharge of units, from which we are going to get rid, there is a figure of 6. So, we should increase the discharge of tens by one. Therefore, when rounding the number 156 to dozens, we get 160.

Consider the example of a fractional number. For example, we are going to round 0.238 to the hundredths. According to rule 1, we must discard the eight, which stands to the right of the rank of hundredths. And according to rule 3 we will have to increase the top three in the discharge of the hundredths by one. As a result, rounding the number 0.238 to the hundredth, we get 0.24.

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