These questions ask for a decimal rounded to a stated number of decimal places or to the nearest whole number. Accuracy comes from marking the kept place and consulting one adjacent digit, rather than rounding repeatedly.
Mark the place, then make one decision
First underline the digit in the requested place. For one decimal place, keep through tenths and inspect hundredths; for two decimal places, keep through hundredths and inspect thousandths; for a whole number, keep the units digit and inspect tenths. If the deciding digit is 0, 1, 2, 3 or 4, leave the final kept digit alone. If it is 5, 6, 7, 8 or 9, add one to the final kept digit. Then remove every digit to its right.
For example, to round 3.761 to one decimal place, keep the 7 in the tenths place and inspect the following 6. Increase the kept digit and write 3.8. Do not first round to hundredths: later digits never get a separate vote. If the kept digit is 9 and must increase, carry left exactly as in whole-number addition. The rounded value may therefore cross a whole-number boundary. When the task states a precision, notation such as a final zero can show that precision even though the numerical value is unchanged.
| Requested place | Final kept place | Deciding place |
|---|---|---|
| Nearest whole number | Units | Tenths |
| One decimal place | Tenths | Hundredths |
| Two decimal places | Hundredths | Thousandths |
Avoid these rounding traps
| Tempting route | How to reject it |
|---|---|
| Round in stages from the far-right digit | This can turn a deciding 4 into a 5 and change the result. Go directly to the requested place and inspect only the next digit. |
| Increase for any nonzero deciding digit | The threshold is 5. A deciding digit from 1 through 4 still leaves the kept digit unchanged. |
| Round down when the deciding digit is exactly 5 | School half-up rounding includes 5 in the increase group, so add one to the final kept digit. |
| Return the wrong number of decimal places | Identify the requested place before calculating. A nearby value at hundredths is not a result rounded to tenths, and a decimal value is not a nearest-whole result. |
Try it
Round the science reading 6.274 to two decimal places and enter the number.
Round 0.985 to one decimal place and enter the number.
Round the length 7.96 to one decimal place and enter the number.