year 8 maths

4G
Finding a percentage and expressing as a percentage
241
ENRICHMENT
– –
21
Two-dimensional percentage increases
+25%
12 cm
20 cm +25%
21 A rectangular photo has dimensions 12 cm by 20 cm .
a What is the area of the photo in cm 2 ?
The dimensions of the photo are increased by 25% .
b What is 25% of 20 cm?
c What are the new dimensions of the photo?
d What is the new area of the photo in cm 2 ?
e What is the increase in the area of the photo?
f What is the percentage increase in the area of the photo?
g What effect did a 25% increase in dimensions have on the area of the photo?
h Can you think of a quick way of calculating the percentage increase in the area of a rectangle
for a given increase in each dimension?
i What would be the percentage increase in the area of a rectangle if the dimensions were:
i increased by 10% ? ii increased by 20% ?
iii increased by 33 1 %? iv increased by 50% ?
3
You might like to draw some rectangles of particular dimensions to assist your understanding of
the increase in percentage area.
j What percentage increase in each dimension would you need to exactly double the area of the
rectangle?
k You might like to explore the percentage increase in the volume of a three-dimensional shape
when each of the dimensions is increased by a certain percentage.
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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