Rounding and Decimals:
Round a Number to a Specified Precision
We may get an answer that has a very long list of decimals, like 3.1415926535897932... We don’t want to have to write that all of the time, but ending it early causes us to lose some precision. 3 is not the same as 3.14, which is not the same as 3.1415. Precision is the number of decimal places you keep on the number. The more you keep, the closer your number is to the correct number. In many problems you’ll be solving in future lessons, you’ll be asked to round your answer to a certain precision.
Video Source (06:41 mins) | Transcript
Remember, when rounding, look at the digit to the right of the place value you want to round to (if you’re rounding to the tenths place, look at the hundredths place), if it’s less than or equal to 4 the place value you are rounding to stays the same. If the place value to the right is greater than or equal to 5, add 1 to the place value you are rounding to.
| Place Value to the Right | How to Round to a Specific Place Value | Example |
|---|---|---|
| 0,1,2,3,4 | Keep the number in the place value you are rounding to the same. | Round \(-17.43\) to nearest tenth: \(-17.4 \) Round 97.432 to the nearest hundredth: 97.43 |
| 5,6,7,8,9 | Increase the number in the place value you are rounding to by 1. | Round 12.59 to the nearest tenth: 12.6 Round 97.436 to the nearest hundredth: 97.44 |
Additional Resources
- Khan Academy: Rounding decimals on the number line (04:22 mins)
Practice Problems
- Round the number 227.18 to the nearest ten.
- Round the number 27070 to the nearest hundred.
- Round the number 47397686 to the nearest million.
- Round the number 0.62968 to the nearest hundredth.
- Round the number 856.861203 to the nearest thousandth.
- Round the number 599.495 to the nearest tenth.
- Round the number 599.995 to the nearest tenth.
