Idea 17of 23Builds onExactly halfway rounds up
The hundredths digit is a shortcut
Can you round to a tenth without drawing the line?
Today you'll discover
- which digit tells the side of halfway
- the 5-or-more rule
- why the rule works
Think first4.36 rounds to 4.4
4.36 rounds to 4.4. Which digit could have told you that without the line?
Decide first, then press Next. Read the blue line about the last digit.
A number line from 4.3 to 4.4 with a dot at 4.36 and 4.4 ringed. A blue line reads: hundredths digit 6, 5 or more, so round up. A dashed halfway mark at 4.35. Then 4.32 with hundredths digit 2, less than 5, rounds to 4.3. The last step shows 7.04.
See the whole ideathe big idea and the key word, in one place
The big idea
Look at the hundredths digit: 5 or more, round the tenth up; less than 5, keep it.
The digit tells the side
Hundredths digit 0 to 4: before halfway, keep the tenth. Hundredths digit 5 to 9: at or past halfway, round up.
- 4.324.3
- 4.354.4
- 4.364.4
Easy to get wrongRounding up changes only the tenths digit; the hundredths is dropped. 4.36 becomes 4.4, not 4.46 or 4.5.
Key word
- hundredths digit
- the second digit after the decimal point; it decides which way to round to a tenth
Ready to use it?
- Round to the nearest tenth using the hundredths digit.
- Spot a rounding mistake and explain it.