Rules For Fractions
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1
2tudent
S
earning
L
entre
C
Rules for fractions
A
S
DDITION AND
UBTRACTION
To add or subtract fractions they must have the same denominator (the bottom value).
Addition and Subtraction with the same denominators
If the denominators are already the same then it is just a matter of either adding or subtracting the numerators (the top
=
=
3
2
3+2
5
value).
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4
4
4
4
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+
Example
+
Addition
−
=
=
−
=
3
2
3−2
1
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4
4
4
4
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Subtraction
Example
Addition and Subtraction with different denominators
If the denominators are different then a common denominator needs to be found. This is most easily done by creating a
common denominator that is the product of the two differing denominators. To achieve this multiply the denominator and
the numerator of each fraction by the opposite denominator. This is actually the same as multiplying 1 and so we aren’t
really changing anything.
+
=
+
=
=
+
=
+
=
3
2
3(3)
2(5)
9+10
19
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5
3
5(3)
3(5)
15
15
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Example
Addition
−
=
−
=
−
=
−
=
=
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2
3
2 5
3 3
10−9
1
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��������
3
5
3 5
5 3
15
15
Subtraction
Example
M
ULTIPLICATION
×
=
=
×
=
4
2
8
4
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7
6
42
21
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To multiply fractions simply multiply the nominators
Example:
and multiply the denominators:
a
D
IVISION
÷
=
×
÷
=
×
2
4
2
7
14
7
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3
7
3
4
12
6
����
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To divide one fraction by another we must flip the
=
=
=
Example:
second fraction and then multiply with the first:
+
=
×
=
P
RACTICE
2
4
3
5
7
3
4
6
1)
2)
÷
=
−
=
7
2
7
3
12
3
12
8
3)
4)
Check your answers on the back.
Rules of Fractions
5/2013 @ SLC
1 of 2
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