Fractions to decimals

Conversions: fractions to decimals

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How to change a fraction to a decimal

Make sure you know the most commonly used fractions as decimals.

If you know what 1/5 is as a decimal, you can work out 3/5 by multiplying by 3.

e.g. 1/5 = 0.2

Therefore 3/5 = 3 x 0.2 = 0.6

So the first step could be to make sure you know:

½ = 0.5

¼ = 0.25 therefore ¾ = 0.75

From ¼ (0.25) you can easily work out 1/8 = 0.125

(In other words 0.25 is divided by 2 because 1/8 is half of ¼)

Useful to know - Part 1:

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Make sure you know these fractions as decimals too:

1/5 = 0.2

1/6 = 0.166

1/8 = 0.125

1/3 = 0.333

You will then be able to calculate other decimals through multiplication e.g. 2/3 = 0.666666….


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1/5 = 0.2 therefore 4/5 = 0.8

1/3 = 0.333 therefore 2/3 = 0.666 (given to 3 decimal places)

From 1/3 you can work out 1/6 = 0.166

In other words 0.333 is divided by 2 because 1/6 is half of 1/3

Knowing a few fractions to decimals by heart, you will then be able to calculate others.


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½ = 0.5

¼ = 0.25 ¾ =

1/3 = 0.333 2/3 =

1/5 = 0.2 2/5 = 3/5 =

1/6 = 0.166 5/6 =

1/8 = 0.125 3/8 = 5/8 =

Knowing the first column, work out the other columns

6Answers on next slide

½ = 0.5

¼ = 0.25 ¾ = 0.75

1/3 = 0.333 2/3 = 0.666

1/5 = 0.2 2/5 = 0.4 3/5 = 0.6

1/6 = 0.166… 5/6 = 0.83

1/8 = 0.125 3/8 = 0.375 5/8 = 0.625

Learn the first column. Work out the other columns

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Fractions to decimals – Option 1

Option 1:

Use the ‘unitary’ method i.e. remembering 1/5 is 0.2 allows us to say

2/5 = 2 x 0.2 = 0.4


Option 1: using the ‘unitary’ method i.e. remembering 1/8 = 0.125 allows us to say

7/8 = 7 x 0.125 = 0.875

Option 2:

Another way to convert 7/8 is to complete the following operation:

7 divided by 8 = 0.875 by what some may remember as ‘long division’.

See this worked out on the next slide.


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Option 2: 7 divided by 8 = 0.875 by what some may remember as ‘long division’ – see below:


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Option 3:

We have just found the answer to 7/8 as a decimal i.e. that

7 divided by 8 = 0.875

Most of us find it much easier to divide by smaller numbers so we could divide

7 by 2 = 3.5 then

3.5 divided by 2 = 1.75 and finally

1.75 divided by 2 = 0.875

This works because 2 x 2 x 2 = 8

See this worked out again on the next slide.


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Option 3: 7 divided by 8 = 0.875 by dividing by 2, then dividing by 2 again and finally diving by 2 yet again. This works because 2x2x2=8.

Conversions: fractions to decimals

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http://www.bbc.co.uk/bitesize/ks2/maths/number/fractions_to_decimals/play/

http://www.mathsisfun.com/converting-fractions-decimals.html

http://www.webmath.com/fract2dec.html

http://www.cimt.plymouth.ac.uk/projects/mepres/book7/bk7i17/bk7_17i2.htm

http://www.mathplayground.com/fractions_convert.html

Need more practice:

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Good luck! 15

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Fractions to decimals