IXL | Estimate population size using proportions

Jerry studies bottlenose dolphins and wants to estimate the population in a certain region. Jerry catches 170 dolphins, marks them, and releases them. Later on, Jerry catches 240 dolphins and observes that 12 of them are marked. To the nearest whole number, what is the best estimate for the dolphin population?

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Learn with an example

question

A group of seventh-grade volunteers helped determine the lizard population of a local park. First, adult volunteers marked 96 lizards. Then, the student volunteers counted a total of 420 lizards in the park, 63 of which were marked. To the nearest whole number, what is the best estimate for the lizard population?

solution

The ratio of marked lizards to total lizards should be about the same in both the sample population and the overall population. You know how many lizards were in the sample and how many of those were marked. You also know the total number of marked lizards.

Set up a proportion.

marked lizards counted

total lizards counted

total marked lizards

estimated lizard population

Plug in the numbers you know and solve for the lizard population,

420

(

420

)

Multiply both sides by

420

(

420

)

Multiply both sides by

420

Simplify

420

Simplify

40,320

Simplify

Divide both sides by 63

640

Divide both sides by 63

The best estimate for the lizard population is 640.

Looking for more? Try these:

Lesson: Proportions

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Teacher tools

Work it out

Not feeling ready yet? These can help:

G.1Solve proportions

L.11Do the ratios form a proportion: word problems

Lesson: Proportions

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