IXL | Estimate population size using proportions

Albert keeps track of the populations of various creatures near a lake. In order to estimate the dragonfly population, he captures 540 dragonflies and marks them with special paint. He releases them, waits a few days, and then captures 570 dragonflies. He notices that 54 of these dragonflies are marked. To the nearest whole number, what is the best estimate for the dragonfly population?

ref_doc_title.

Learn with an example

question

Marmots are animals that live in burrows underground. They are a good target species for studies about population changes over time because they don't migrate. Professor Monroe's research group traps 170 marmots and tags them. They return the tagged marmots to the wild and, a week later, trap 920 marmots. Of those marmots, 68 are marked. To the nearest whole number, what is the best estimate for the marmot population?

solution

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

Set up a proportion.

marked marmots counted

total marmots counted

total marked marmots

estimated marmot population

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

920

170

920

(

920

)

Multiply both sides by

920

170

(

920

)

Multiply both sides by

920

Simplify

170

920

Simplify

156,400

Simplify

Divide both sides by 68

2,300

Divide both sides by 68

The best estimate for the marmot population is 2,300.

Looking for more? Try these:

Lesson: Proportions

$Confetti$

Excellent!

Now entering the Challenge Zone—are you ready?

Teacher tools

Work it out

Not feeling ready yet? These can help:

L.12Solve proportions

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

Lesson: Proportions

Excellent! You got that right!

Jumping to level 1 of 1

Excellent!