year 8 maths

204 Chapter 4 Fractions, decimals, percentages and financial mathematics
Key ideas
■ Common multiple (CM) and lowest common multiple (LCM)
• A common multiple is found by multiplying whole numbers together.
• The LCM is found by multiplying the whole numbers together and then dividing by the
HCF of the whole numbers.
For example, consider the whole numbers 4 and 6 .
A common multiple is 24 (i.e. 4 × 6) . The LCM is 12 (
i.e. 4 × 6
2 ) .
• The lowest common denominator (LCD) is the lowest common multiple (LCM) of the
denominators.
■ Multiplying fractions
Example:
1
2 of 3
4 = 1 2 × 3 4
= 3 8
1
4
3
4 shaded
1
4
3
4
1
4
1
8
1
8
1
8
1
8
1
8
1
8
is one-half of
• Denominators do not need to be the same before you can proceed with fraction
multiplication.
• Simply multiply the numerators together
and multiply the denominators together.
• Mixed numerals must be converted to
improper fractions before you can proceed.
• If possible, simplify or ‘cancel’ fractions
before multiplying.
3
8
3
4
Example:
2
3 × 5 9 = 2 × 5
3 × 9 = 10
27
Multiply numerators together.
Multiply denominators together.
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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