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How do you solve problems?
LEARNING
STANDARDS
15 Solve problems involving
ratios, rates and
A farmer uses the capture, mark, release and recapture proportions, including
method to estimate the population of snails in his vegetable making estimations.
farm. He captures 24 snails and marks on the shell of each of
them. Then, he releases them back into the farm. Two weeks
later, he captures randomly 30 snails and finds that 5 of them
are marked. He uses the following proportion to estimate the CHAPTER
population of snails in the vegetable farm.
4
Number of marked snails Number of snails which are captured and marked
=
Number of recaptured snails Population of snails in the vegetable farm

Estimate the population of snails in the vegetable farm.

Let the population of snails in the farm = x

Number of marked snails Number of snails which are captured and marked
=
Number of recaptured snails Population of snails in the vegetable farm

5 24
=
30 x
1 5 24
=
30 x
6
× 24

1 24 How would you find
=
6 x the value of x if you do
not change 5 in its
× 24 30

x = 6 × 24 simplest form?
= 144

The farmer estimates that there are 144 snails in the vegetable farm.

id ou now

By knowing the pest population in a certain habitat, scientists can estimate the optimum
use of pesticides so that the ecological balance can be maintained without affecting the
survival of other living organisms.

91
Ratios, Rates and Proportions

04 TB Math F1.indd 91 11/10/16 12:12 PM