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Maths

Approximation

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Rounding to a given number of places

Counting decimal places

Decimal places are counted from the decimal point:

5.743

So, the number 5.1492 has four decimal places and 4.34 has two decimal places.

To round a number to a given number of decimal places, look at the number in the next decimal place.

  • If it's less than 5 round down
  • If it's 5 or more, round up
Question

Q1. Round 7.2648 to 2 decimal places (d.p.)

Q2. Round 8.352 to 1 decimal place

Answer

A1.

7.2648

To round to two decimal places, look at the number in the third decimal place. It's a 4, so round down.

Therefore, 7.2648 = 7.26 (2 d.p.)

A2.

8.352

To round to one decimal place, look at the number in the second decimal place. It's a 5, so round up.

Therefore, 8.352 = 8.4 (1 d.p.)

To round a number to a given number of decimal places then the answer must have that number of decimal places, even if you have to add some zeros.

For example, rounding 3.40021 to two decimal places gives 3.40 (2 d.p.).

You need to write both decimal places, even though the second number is a zero, to show you rounded to two decimal places.

Remember to look at the number after the one you're interested in. If it's less than 5, round down. If it's 5 or more, round up.

Activity

Approximation activity

Round up, round up and try this activity!

Play

Elemental

Can you conquer the elements?

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