3.1Rounding Off Whole Numbers and Decimals
Rounding whole numbers
- Identify the digit in the required place (tens, hundreds, thousands, etc.).
- Examine the next digit on the right.
- If it is 5 or more, round up. If it is less than 5, round down.
- Replace all digits to the right with zeros.
- Always say how far you rounded, as in (to 1 d.p.). Write it with ; the bracket is the part that must never be missing.
Rounding a population figure
Singapore's population in 2023 was 5 917 600. Round this to the nearest 100 000.
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The digit in the hundred-thousands place is .
The next digit is (less than 5), so round down.
(to the nearest ).
Now you try
Round 51 620 to the nearest 1000.
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The thousands digit is 1, and the digit to its right is 6.
Since 6 5, round up: the thousands digit becomes 2.
51 620 rounded to the nearest 1000 is .
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Rounding decimals
To round to a given number of decimal places, look at the first digit you are dropping.
Rounding a measurement
A plank of wood is measured as m. Round this to 2 decimal places.
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The digit in the hundredths place is .
The next digit is (less than 5), so round down.
m (to 2 d.p.).
Now you try
Correct to 1 decimal place.
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Identify the digit in the tenths place.
Examine the next digit: it is 1.
Since 1 5, we round down.
(to 1 decimal place)
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