1. A manufacturer receives parts from two suppliers. An SRS of 400 parts from supplier 1 finds 20 defective. An SRS of 100 parts from supplier 2 finds 10 defective. Let p1 and p2 be the proportion of all parts from suppliers 1 and 2, respectively, that are defective. Is there evidence of a difference in the proportion of defective parts produced by the two suppliers? To determine this, you test the hypotheses
H 0: p1 = p2, Ha: p1 ≠ p2.
The P-value of your test is
A. 0.1164.
B. 0.0602.
C. 0.0301.
2. A sociologist is studying the effect on the divorce rate of having children within the first three years of marriage. From city marriage records she selects a random sample of 400 couples who were married between 1985 and 1990 for the first time, with both members of the couple between 20 and 25. Of the 400 couples, 220 had at least one child within the first three years of marriage. Of the couples who had children, 83 were divorced within 5 years, while in the couples who didn't have children within three years only 52 were divorced. Suppose p1 is the proportion of couples married in this time-frame who had a child within the first three years and were divorced within five years and p2 is the proportion of couples married in this time-frame who did not have a child within the first three years and were divorced within five years. The sociologist hypothesized that having children early would increase the divorce rate. She tested the one-sided alternative and obtained a P-value of 0.0314. The correct conclusion is that
A. if you want to decrease your chances of getting divorced, it is best to wait several years before having children.
B. there is evidence of an association between divorce rate and having children early in a marriage.
C. if you want to decrease your chances of getting divorced, it is best not to marry until you are closer to 30 years old.
3. A bank wants to get new customers for their credit card. They try two different approaches in their marketing campaign. The first promises a "cash back" reward; the second promises low interest rates. A sample of 500 people are mailed the first brochure; of these, 100 get the credit card. A separate sample of 500 people are mailed the second brochure; 125 get the credit card. Are the two campaigns equally attractive to customers? Find the test statistic.
A. z = -1.89
B. z = 2.80
C. z = 0.25