7th Grade Math

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Proportions

PART A BC

Multi-Part

Lesson 1

GLE 0706.2.3

Develop an understanding

of and apply proportionality.

Also addresses GLE 0706.1.7,

SPI 0706.2.7.

Main Idea

Use proportions to

estimate populations.

Wildlife Sampling

Naturalists can estimate the

population in a wildlife preserve

by using the capture-recapture

technique. You will model this

technique using dried beans in a

bowl to represent bears in a forest.

Fill a small bowl with dried beans. Scoop out some of

the beans. These represent the original captured bears.

Count and record the number of beans. Mark each bean

with an × on both sides. Then return these beans to

the bowl and mix well.

Scoop another cup of Trial Sample Recaptured P

A

B



Total

beans from the bowl

and count them. This

is the sample for

Trial A. Count the

beans with the ×s.

These are the

recaptured bears. Record both numbers in a table.

Use the proportion below to estimate the total number

of beans in the bowl. This represents the total

population P. Record the value of P in the table.

captured

__total population ( (^) P) =
recaptured
_sample
Return all of the beans to the bowl.
Repeat Steps 2–4 nine times.
the Results

1. ESTIMATION Find the average of the estimates in column P. Is this
   a good estimate of the number of beans in the bowl? Explain your
   reasoning.


2. Count the actual number of beans in the bowl. How does this
   number compare to your estimate?

D E

Lesson 1E Proportions 281

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