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 currency 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 13 packs should be ordered to ensure every staff member gets a bottle of water.
