1.- Monthly cell phone bills rounded to the nearest whole dollar were recorded for 12 randomly selected individuals. The results are:

Create a stemplot of these cell phone bills.

56

50

63

70

60

42

49

52

58

19

64

From your stemplot above, explain if it is or is not safe to use a t-procedure to analyze these data.

2.- Annual earnings of college graduates aged 25-to-34 was recorded in a simple random sample of 40 males and a simple random sample of 35 females. The summary statistics are:

Construct a 95% confidence interval for the mean difference in male and female annual salaries, rounded to the nearest dollar.

Interpret the confidence interval above.

3.- Nationally, the proportion of high school graduates who take the SAT is between .3 and .7. How large a sample is necessary to estimate the true proportion of high school graduates who take the SAT within 2.5 percentage points (i.e. 0.025) with 90% confidence?

4.- A dietician claims that 60% of people in the U.S. are trying to avoid trans fats in their diets. You randomly select 100 people and find that 58 of them are trying to avoid trans fats. Use this information for questions (a) and (b) below.

(a) In a test of significance seeking evidence against the dietician's claim, the alternative hypothesis is A)Ha:p= 58

B)Ha:= 60 C) Ha: p = 0.58 D) Ha: p = 0.60

(b) Using the appropriate table, if the test statistic was -0.41 the p-value would be: A) 0.25< p <0.5

B) p<0.25

C) p = 0.3409 D) p = 0.6818

5.- SHOW WORK. An SRS of 18 recent birth records at the local hospital was selected. In the sample, the average birth weight was 119.6 ounces and the standard deviation was 6.5 ounces. Assume that in the population of all babies born in this hospital, the birth weights follow a Normal distribution, with mean . The standard error of the mean is

A) 6.50 ounces B) 1.53 ounces C) 0.36 ounces D) 0.02 ounces

6.- Do SAT coaching classes work? Do they help students to improve their test scores? Four students were selected randomly from all of the students that completed an SAT coaching class. For each student, we recorded their first SAT score (before the class) and their second SAT score (after the coaching class).

To analyze these data we should use A) the one-sample t test.

First SAT score Second SAT score

920 830 1010 800

960 910 1000 980

B) the matched pairs t test.

C) the two-sample t test.

D) Any of the above tests are valid. It just needs to be at since is unknown.

7.- In a test of significance, the P-value is

A) the probability the null hypothesis is true.

B) the probability the null hypothesis is false.

C) the probability, assuming the null hypothesis is true, that the test statistic will take a value at least as extreme as that actually observed.

D) the probability, assuming the null hypothesis is false, that the test statistic will take a value at least as extreme as that actually observed.

8.- If conditions for inference were met and the true population standard deviation () was known, the test statistic used for inference for a single true mean () of a population is:

A) p B) 2 C) t D) z

9.- The variability of a statistic is described by

A) the spread of its sampling distribution.

B) the amount of bias present.

C) the vagueness in the wording of the question used to collect the sample data. D) the stability of the population it describes.

10.- You conduct a statistical test of hypotheses and find that the null hypothesis is statistically significant at level = 0.05. You may conclude that

A) the test would also be significant at level = 0.10. B) the test would also be significant at level = 0.01. C) both a and b are true.

D) neither a nor b is true.