Fractions Worksheet Page 14
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36Fractions
3.4
The four rules for fractions
You can add, subtract, multiply and divide fractions.
Adding fractions
�
�
When fractions have the same denominator it is easy to
add them. You simply add the numerators.
2
3
5
For example,
1
5
7
7
7
Notice that you do not add the denominators.
When fractions do not have the same denominator you
Equivalent fractions are in
need to use equivalent fractions to change one or both
Section 3.1
fractions so that the denominators are the same.
2
3
For example,
1
�2
5
10
Multiplying both
numerator and
2
4
2
4
can be written as
�
5
10
denominator
5
10
by 2.
4
3
7
So the addition becomes
1
5
�2
10
10
10
To add fractions, you need to change them to equivalent
fractions with the same denominator.
The denominators are 3 and 5. Look
for a number that is in the 3-times
10
EXAMPLE
and 5-times tables. 15 is in both.
2
4
Work out
.
�5
�3
1
3
5
2
10
4
12
�
�
2
4
10
12
3
15
5
15
1
5
1
3
5
15
15
22
�5
�3
5
15
7
5 1
See Section 3.3, Improper fractions
15
and mixed numbers.
11
EXAMPLE
1
5
Work out 3
1 1
Write mixed numbers as improper
.
4
6
fractions first.
Method 1
1
5
13
11
Multiplying by 3 and by 2 to get a
3
1 1
5
1
4
6
4
6
denominator of 12 in each fraction.
39
22
5
1
12
12
61
Always give your answer as a mixed
5
12
number.
1
5 5
12
Continued...
Number 73
M03_CMC_SB_IGCSE_6850_U03.indd 73
9/6/09 16:45:08
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