Topic 7 Percentages With Answer Key - Math Quest 7 Page 28
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40NUMBER AND ALGEBRA
3
Find 5% of the original amount by
5% = $4.60 ÷ 2
halving 10%, that is, halving $4.60.
= $2.30
4
Find 25% by adding the 20% and
25% = $9.20 + $2.30
the 5%, that is, $9.20 and $2.30.
= $11.50
WORKED EXAMPLE 20
WORKED EXAMPLE 20
WORKED EXAMPLE 20
Find:
12% of $53
43% of $120.
Round answers to the nearest 5 cents.
a
b
THINK
WRITE
a
1
Break up the percentage into
a
12% = 10% + 2 × 1%
lots of 10% and 1%.
2
Find 10% of the amount.
10% of $53 = $5.30
Find 1% of the amount and then double it.
1% of $53 = 0.53
3
2% of $53 = 2 × 0.53
= $1.06
4
Find 12% of the amount by adding 10%
12% of $53 = $5.30 + $1.06
and 2% of the amount.
= $6.36
Another way to write this
solution would be:
12% of $53 = 10% of $53
+ 2 × 1% of $53
= $5.30 + 2 × $0.53
= $6.36
5
Round to the nearest 5 cents.
≈ $6.35
To nd 43%, nd 4 × 10% + 3 × 1%.
43% of $120 = 4 × 10% of $120
b
b
+ 3 × 1% of $120
= 4 × $12
+ 3 × $1.20
= $48 + $3.60
= $51.60
Exercise 7.7 Common percentages
and short cuts
INDIVIDUAL PATHWAYS
REFLECTION
PRACTISE
CONSOLIDATE
MASTER
Why is it important to be able
Questions:
Questions:
Questions:
to quickly evaluate common
1–8, 12, 15, 17, 21
1a–l, 2a–j, 3a–h, 4a–f, 5a–f,
1q–x, 2m–t, 3i–o, 4i–l, 5i–l,
percentages mentally?
6a–i, 7a–i, 8, 9, 12, 15, 18, 21
6m–r, 7m–r, 9–21
Individual pathway interactivity
int-4348
Topic 7 • Percentages
271
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