What is rounding off?
Rounding off changes a number to a nearby, tidier number. We can round to the nearest ten or the nearest hundred to make numbers easier to use. Rounded numbers are quicker to add in our heads and are handy when we only need a rough amount.
Key idea
Look at the next digit. If it is 5 or more, round up. If it is less than 5, round down (stay the same).
Rounding to the nearest ten
Round 47 to the nearest ten. The ones digit is 7, which is 5 or more, so we round up to 50.
Worked example
Round 128 to the nearest hundred. Look at the tens digit, 2. It is less than 5, so we round down. 128 becomes 100. If it were 152, the tens digit 5 would make us round up to 200.
Remember
- 5 or more, round up.
- Less than 5, round down.
- Check the next digit each time.