Download Working with decimals

Key skills resource sheet
Working with decimals
Introduction
What are decimals?
Decimals are fractions expressed as tenths, hundredths, thousands, etc. Decimals may be easier to
work with than common fractions.
Decimals use a decimal point to separate the whole number from the fractional bit. For example,
6.2 is 6 whole ones and two tenths (2/10).
If a fraction is expressed in tenths, hundredths, thousands, etc. it can be written as a decimal easily.
For example:
6
10 = 0.6
27
100 = 0.27
349
1000 = 0.349
If the fraction is not expressed in tenths etc. then you can calculate the decimal fraction by dividing
the numerator (top number) by the denominator (bottom number). For example:
3
5 = 3/5 = 0.6
7
8 = 7/8 = 0.875
3
4 = 3/4 = 0.75
Calculating with decimals is much easier than with common fractions.
Adding and subtracting decimals
When adding and subtracting decimals, always keep the decimal point in a vertical line. For
example:
11.36
101.1
+ 0.275
112.735
©Crown Copyright 2000
–
67.54
2.13
65.41
Produced with assistance from the DfEE Key Skills Support Programme
Multiplying decimals
To multiply decimals:
1 Ignore the decimal point and multiply the numbers as if they were whole numbers.
2 Then work out where to put the decimal point by counting how many figures (including 0s) there
are to the right of the decimal point in each number you are multiplying.
3 These added together give you the number of figures that must be to the right of the decimal
point in the answer.
Example 1:
2.4
x 3.9
216
720
936
Example 2:
12.6
x 1.27
882
2520
12600
16002
©Crown Copyright 2000
There is one figure to the
right of the decimal point
There is one figure to the
right of the decimal point
So in total there are two
figures to the right of the
decimal point
Now put the decimal point with two figures to the right of it: 9.36
There is one figure to the
right of the decimal point
There are two figures to the
right of the decimal point
So in total there are three
figures to the right of the
decimal point
Put the decimal point with three figures to the right of it: 16.002
Produced with assistance from the DfEE Key Skills Support Programme