AP Stats Benchmark Review

Le the random variable X represent the amount of money Carl makes tutoring statistics students in the summer.  Assume that X is Normal with mean $240 and standard deviation $60.  The probability is approximately 0.6 that, in a randomly selected summer, Carl will make less than about

• $144

• $216

• $255

• $30

The time it takes students to complete a statistics quiz has a mean of 20.5 minutes and a standard deviation of 15.4 minutes.  What is the probability that a random sample of 40 students will have a mean completion time greater than 25 minutes?

• 0.9678

• 0.0322

• 0.0344

• 0.3851

A fair coin (one for which both the probability of heads and the probability of tails are 0.5) is tossed 60 times.  The probability that more than 1/3 of the tosses are heads is closest to 

• 0.9951

• 0.33

• 0.109

• 0.09

The incomes in a certain large population of college teachers have a normal distribution with mean $60,000 and standard deviation $5000.  Four teachers are selected at random from this population to serve on a salary review committee.  What is the probability that their average salary exceeds $65,000?

• 0.0228

• 0.1587

• 0.8413

• 0.9772

I collect a random sample of size n from a population and from the data collected compute a 95% confidence interval for the mean of the population.  Which of the following would produce a wider confidence interval, based on these same data?

• Use a larger confidence level

• Use a smaller confidence level

• Use the same confidence level, but compute the interval n times.  Approximately 5% of these intervals will be larger

• Increase the sample size

You are told that the proportion of those who answered "yes" to a poll about internet use is 0.70, and that the standard error is 0.0459.  The sample size is

• 50

• 99

• 100

• 200

The standardized test scores of 16 students have mean x̄ = 200 and standard deviation s = 20.  What is the standard error of x̄?

• 20

• 10

• 5

• 1.25

In your top dresser drawer are 6 blue socks and 10 grey socks, unpaired and mixed up.  One dark morning you pull two socks from the drawer (without replacement, of course!)  What is the probability that the two socks match?

• 0.075

• 0.375

• 0.450

• 0.500

• I
• II
• III
• I, II, and III

• The slope decreased and the r² increased.
• The slope increased and the r² decreased.
• The slope decreased but r² remained the same.
• Both slope and r² remained the same.