# Multiple Choice Answers

1.  The owner of Limp Pines Resort wanted to know the average age of its clients. A random sample of 25 tourists is taken. It shows a mean age of 46 years with a standard deviation of 5 years. The width of a 98 percent CI for the true mean client age is approximately.
A)  ± 2.06 years.
B)  ± 2.33 years.
C)  ± 2.49 years.
D)  ± 2.79 years.

2.   The standard error of the mean decreases when
A)  the sample size decreases.
B)  the standard deviation increases if n is constant.
C)  the standard deviation decreases and n increases.
D)  the population size decreases

3.   A poll showed that 48 out of 120 randomly chosen graduates of California medical schools last year intended to specialize in family practice.  What is the width of a 90% confidence interval for the proportion that plan to specialize in family practice?
A)  ± .04472
B)  ± .07357
C)  ± .08765
D)  ± .08944

4.   A company wants to estimate the time its trucks take to drive from city A to city B.  Assume that the standard deviation is known to equal 12 minutes.  What is the sample size required in order that the probability of making an error of more than 2 minutes will not exceed 5 percent?
A)  12 observations
B)  139 observations
C)  36 observations
D)  129 observations

5.   Which of the following is incorrect?
A)  The level of significance refers to the probability of making a Type I error.
B)  In assessing possible error, a low a and b will lead to the selection of a higher sample size.
C)  The probability of rejecting a true null hypothesis increases as the sample size increases.
D)  When Type I error increases, Type II error must decrease

6.  The Jolly Blue Giant Health Insurance Company guideline says that average hospitalization for a triple hernia operation should not exceed 3 days.  A diligent auditor studied records of 16 randomly chosen triple hernia operations at HackMore Hospital, and found a mean hospital stay of 4 days with a standard deviation of 2 days.  “Aha!” she cried, “I have uncovered a violation of the guidelines.”  Use a right-tail test at a = .025.

The value of the test statistic is
A)  2.080
B)  0.481
C)  1.866
D)  2.000

7.  Dullco Manufacturing claims that its alkaline batteries last forty hours on average in a certain type of portable CD player.  Tests on a random sample of 18 batteries from a day’s production run of 2,850 batteries showed a mean battery life of 37.8 hours with a standard deviation of 5.4 hours. In determining the p-value for reporting the study’s findings, which of the following is true?
A)  The p-value is less than .05.
B)  The p-value is equal to a.
C)  The p-value is greater than .05.
D)  The p-value cannot be determined without specifying a.

8.  A TV special said there is a 10 percent incidence of sexually transmitted disease (STD) among all U.S. teens.  A reporter for the Rockville Bugle, looking for a story, surveyed 260 randomly chosen teenagers, and found that 39 had been to a clinic for STD treatment.  Use a right-tail test at a = .05.

The test statistic is
A)  2.687
B)  2.758
C)  .0256
D)  2.258