Federal law under Title 49 of the United States Code, Chapter 301, Motor Vehicle Safety Standard took

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Chapter11: Data Analysis And Probability
Section: Chapter Questions
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  1. Federal law under Title 49 of the United States Code, Chapter 301, Motor Vehicle Safety Standard took effect on January 1, 1968 and required all vehicles (except buses) to be fitted with seat belts in all designated seating positions. While most states have laws requiring seat belt use today, some people still do not “buckle up.”  Let’s assume that 90 % of drivers do “buckle up.”  If drivers are randomly stopped to check seat belt usage, answer the following questions and show your work.

 

  1. If they stop 30 cars during the first hour, find the mean and standard deviation of the number of drivers not expected to be wearing seatbelts?

 

  1.  If they stop 120 cars during this safety check, what is the probability they find at least 12 drivers not wearing seatbelts?
Expert Solution
Step 1

Let the random x denote the number of drivers not wearing seat belts.

Given that 90% buckle up.

The percentage of drivers do not wearing seat belt is,

p= 100- ( % Of wearing seat belts)

  = 100-90

= 10%

That is, p=10%=10/100=0.10

They stopped first 30 cars. That is, n=30

Here x follows Binomial distribution with n=30 and  p=0.10.

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