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Fractions Review
GCF and LCM
1)
GCF: Greatest common factor
Steps: List the factors of all numbers using bridges (use your divisibility rules and
check all the numbers).
Find the greatest common factor.
LCM: Least common multiple
Steps: List the multiples of all numbers
Find the least common multiple
Example: Find GCF and LCM for 24, 48 and 72
GCF
24: 1, 2, 3, 4, 6, 8, 12, 24
48: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48
Greatest Common Factor is 24
72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72
LCM
24: 24, 48, 72, 96, 120, 144
48: 48, 96, 144, 192
Least Common Multiple is 144
72: 72, 144, 216
Try these
1) 12 and 30
GCF=
LCM=
2) 9 and 21
GCF=
LCM=
3) 15 and 18
GCF=
LCM=
WRITING EQUIVALENT FRACTIONS
To write equivalent fractions, we need to multiply or divide numerator and denominator by the
same number.
EXAMPLE:
16 16 x3 48


20 20 x3 60
So
or
16 16  4 4


20 20  4 5
16
48
4
is equivalent to
and
20
5
60
You can decide whether two fractions or equivalent or not by determining which number
numerator and denominator are multiplied or divided by. If it is not obvious, simplify both
fractions to check for simplest form of both fractions.
Example:
42
7
and
42 is divided by 6 to get 7, whereas 60 is divided by 4 to get 15. So these two
60
15
fractions are not equivalent.
Try these
20
18
and
1)
try to simplify these fractions to determine = or not.
60
54
2)
34
2
and
85
5
3)
8
24
and
10
40
4)
54
9
and
80
12