Page 104 - Cambridge+Checkpoint+Mathematics+Coursebook+9

11 Percentages

Two scientists measure the area covered by weed on a lake. Key words
It covers 10 m .
2
Make sure you learn and
understand these key words:
increase
decrease
profit

loss
discount
interest
tax

!ey measure it one week later and it covers 14 m . Each scientist makes a hypothesis.
2
Scientist X says the increaseis 4 m . He thinks it will increase by 4 m every week.
2

2

A"er two weeks there will be 18 m . A" er three weeks there will be 22 m . A" er four weeks there
2
2
will be 26 m .
2
Scientist Y says the increase is 40%.
4
=

!is is because 10 × 100 40%.
She thinks the weed will increase by 40% each week.
60
A"er two weeks the area will be 50

14 + 40% of 14 = 14 + 5.6 = 19.6 m . 40
2

A"er three weeks the area will be Area (square metres) 30 Scientist X
19.6 + 40% of 19.6 = 19.6 + 7.84 = 27.44 m . 20 Scientist Y
2
!is graph shows their predictions. 10

How can they decide who is right? 0
0 2 4 6
Weeks
In this unit you will learn more about using percentages.
Make sure you can remember the equivalences between
simple fractions, decimals and percentages.

1
1
Fraction 1 1 1 3 1 10 100 1 2
4
2
3
5
3
4
Decimal 1 0.5 0.25 0.75 0.2 0.1 0.01 0.33… 0.66…
2
1
Percentage 100% 50% 25% 75% 20% 10% 1% 33 % 66 %
3
3
11 Percentages 103