7th Grade Math

474 Probability and Predictions

A valid sampling method uses unbiased samples. If a sampling

method is valid, you can make generalizations about the population.

Use Sampling to Predict

STORES A store sells 4 styles of pants: jeans, Type Number

Jeans 25

Capris 10

Cargos 8

Khakis 7

capris, cargos, and khakis. The store workers

survey 50 customers at random. The survey

responses are indicated at the right. If

450 pairs of pants are to be ordered, how

many should be jeans?

First, determine whether the sample method is valid. The sample

is a simple random sample since customers were randomly

selected. Thus, the sample method is valid.

_^25

50 or 50% of the customers prefer jeans. So, find 50% of 450.

0.5 × 450 = 225, so about 225 pairs of jeans should be ordered.

b. RECREATION An instructor at a swimming pool asked her

students if they would be interested in an advanced swimming

course, and 60% stated that they would. Is the sample method

valid? If so, suppose there are 870 pool members. How many

people can the instructor expect to take the course?

Determine whether each conclusion is valid. Justify your answer.

1. To determine how much money the average American family spends to
   cool their home, 100 Alaskan households are surveyed at random. Of the
   households, 85 said that they spend less than $75 per month on cooling.
   The researcher concluded that the average American household spends
   less than $75 on cooling per month.


2. To determine the most important company benefit, one out of every five
   employees is chosen at random. Medical insurance was listed as the most
   important benefit by 67% of the employees. The company managers
   conclude that medical insurance should be provided to all employees.

Example 3 33 GOLF Zach is trying to decide which of

three different golf courses is the best. He

randomly surveyed people at a golf store

and recorded the results in the table. Is

the sample method valid? If so, suppose

Zach surveyed 150 more people. How

many people would be expected to vote

for Rolling Meadows?

Examples 1 and 2

Course Number

Whispering Trail 10

Tall Pines 8

Rolling Meadows 7

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