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Maths

Rounding and estimating

Decimal places

Sometimes, rather than rounding off to the nearest whole number, you might need to be a little more accurate. You might need to include some of the digits after the decimal point.

In these cases, we can round off the number up to a certain number of decimal places.

Do not confuse this with rounding off using significant figures, as this is slightly different!

Remember

The same rules for rounding up apply here:

  • 5 or more, we 'round up'.
  • 4 or less, it stays as it is.
Question

Write 2.6470588 to 2 decimal places (dp).

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Answer

Did you get the answer 2.65? You needed to round up. We want 2 decimal places.

Look at the 2nd decimal digit.

The 2nd decimal digit is 4. So the number lies between 2.64 and 2.65

Look at the next digit.

The next digit is 7, so we have to round up. So the answer is 2.65 (2 dp).

Question

On a calculator, work out So 3 over 5 = 6 over 10, giving your answer correct to one decimal place.

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Answer

On a calculator, work out So 3 over 5 = 6 over 10 = 7.874007874...

We need one decimal place. That means one number after the decimal point. The 1st number after the decimal point is 8. This means the answer lies between 7.8 and 7.9. The next digit is 7. This means we have to round up.

So the answer is So 3 over 5 = 6 over 10 = 7.9 to 1 dp.

Question

Round off the number 3.9762645 to 1 dp.

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Answer

The number lies between 3.9 and 4.0. The 7 after the 9 means you have to round up. So the answer is 4.0

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