Quiz Chapter 18-19

AP Statistics
Name: _____________________________
Quiz Chapter 18-19 35 Date: ___________ My name affirms my honor.
1. It is generally believed that electrical problems affect about 14% of new cars. An
automobile mechanic conducts diagnostic tests on 128 new cars.
a) Describe the sampling distribution for the sample proportion by naming the model
and stating the mean and standard deviation. Check conditions. (8 pts)
b) Using the 68-95-99.7% Rule, draw and label the distribution of the proportion of
these cars that will have electrical problems. (4 pts)
c) What is the probability that in this group of 128 cars, over 18% will be found to have
electrical problems? (4 pts)

2. A statistics professor asked her students whether or not they were registered to vote. In a
sample of 50 of her students (randomly sampled from her 700 students), 35 said they
were registered to vote.
a) Find a 95% confidence interval for the true proportion of the professor’s students who
were registered to vote. (Make sure to check any necessary conditions.) (8 pts)
b) State your conclusion in the context of the problem. (2 pts)
c) Explain what 95% confidence means. (2 pts)
d) According to a September 2004 Gallup poll, about 73% of 18- to 29-year-olds said
they were registered to vote. Does the 73% figure seem reasonable for the professor’s
students? Explain using your confidence interval. (2 pts)
e) If the professor only knew the information from the September 2004 Gallup poll (see
part d) and wanted to estimate the percentage of her students who were registered to vote
to within margin of error with 95% confidence, how many students should she
sample? (5 pts)