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Rounding numbers

A rounded number has about the same value as the number you started with but is less exact.

Rules for rounding

  • Identify the place value you are rounding to. For example for rounding currentcy to the nearest cent use 2 decimal places (hundredths).
  • Look at the digit to the right of this place:
    • If this number is less than 5 (0, 1, 2, 3, 4) you leave your last digit as it is.
    • If it is 5 or more (5, 6, 7, 8, 9) you increase the value of your last digit by one.
    • Any digits after your place become zeros or are dropped off if they are to the right of the decimal point.

Examples:

1.    Round to the nearest cent: Rounded
  (a)  $ 72.3483844 $ 72.35
  (b)  $ 104.2309 $ 104.23
  (c)  $2.3981007 $ 2.40
2.    Round to the nearest 100:
   (a)  1,237 1,200
   (b)  127,899 127,900
   (c)   945,555,972 945,556,000

Rounding to the nearest whole number

The usual rules for rounding apply in most situations when rounding to a whole number. However, in some situations the correct answer will always require rounding up.

For example:
Bottled water is sold in packs of 12. How many packs need to be ordered to ensure that all 147 staff get a bottle of water?

Calculation 147 ÷ 12 = 12.25
Conventional rounding would mean this number would be rounded down to 12.

But notice that 12 x 12 = 144 so 3 staff would miss out.
The correct answer is that that 13 packs should be ordered to ensure every staff member gets a bottle of water.