17. A study was commissioned to compare the housing costs of two growing cities. The goal of the study was to estimate the difference in the average housing costs (as measured in price per square foot) of the two cities. Two pilot samples were taken and yielded the following information: Use this information to determine how large the sample sizes must be in order to estimate the true difference in the average housing costs of the two cities to within $1.25. Assume that equal sample sizes are desired and a 95% reliability level is essential.
(A)nl =n2 =76
(B) n1 =n2=84
(C)n1 =n2=119
(D)n1 =n2= 25

1. The scores of individual students on the American College Testing (ACT) Program composite college entrance examination have a normal distribution with mean 18.6 and standard deviation 6.0. At Northside High, 36 seniors take the test. If the scores at this school have the same distribution as national scores, what is the mean of the sampling distribution of the average (sample mean) score for the 36 students? (A)1.0 (B) 3.1 (C)6.0 (D)18.6

2. I take a random sample survey of size n from a population that has mean 80 and standard deviation20. How big should n be so that the sampling distribution of has standard deviation 1? (A)400 (B) 20 (C)Approximately 5 (D)Cannot be determined unless we know the population follows a normal distribution.

3. A researcher is interested in the size of the current balance of credit card holders. To estimate this, he obtains the size of the current balance of a random sample of 25 credit card holders. A 90% confidence interval for the mean current balance of credit card holders is found to be S662.72±$44.70. Which of the following would produce a contidence interval with a smaller margin of etror than this 90% confidence interval? (A)Obtain the balances of only five credit card holders rather than 25, because five are likely to be more uniform than 25. (B) Obtain the balances of 100 credit card holders rather than 25. (C)Computer a 99% confidence interval rather than a 90% confidence interval. The increase in confidence indicates that we have a better interval. (D)None of the above.

4. In a large city, the percent of total spending that households devote to housing is normally distributed, with mean u and standard deviation o= 9%. I select a simple random sample of four young households and determine the percent of their total spending that is devoted to housing. The four percentages are  33%  39%  32%  36% Based on these data, a 99% confidence interval forμis(A)35%±5.78%. (B)35%±8.82% (C)35%±11.59% (D)35%±23.18% 

5. An engineer designs an improved light bulb. The previous design had an average lifetime of 1200 hours. The new bulb has a lifetime of 1201 hours, using a sample of 2000 bulbs. Although the difference is quite small, the cffect is statistically significant. The explanation is (A)that new designs typically have more variability than standard designs. (B) that the sample size is very large. (C)that the mean of 1200 is large. (D)all of the above.

6. The sum of squares for error is (A)1021.8 (B)14512.0 (C)20853.5(D)147144.0

7. In the ANOVA table, the test for the main cffect of DESIGN has a P.-value of .613. This indicates that (A)sales probably vary considerably for the different designs. (B) for about 61.3% of the samples, there was a difference in the effect of design. (C)for about 61.3% of the samples, there was no difference in the effect of design. (D)None of the above is true.

8. the numerical value of the F statistic for testing interaction is(A)0.59(B)1.70(C)3.40(D)202.33

9. Investing is a game for chance. Suppose there is a 40% chance that a risky stock investment will end up in a total loss of your investment. Because the rewards are so high, you decide to invest in four independent risky stocks. Find the probability that at least one of your investments becomes a total loss. (A).0256 (B).40 (C).9744 (D).8704

10. The on-line access computer service industry is growing at an extraordinary rate. Current estimates suggest that only 20% of the home-based computers have access to on-line services. This number is expected to grow quickly over the next five years. Suppose 25 people with home-based computers were randomly and independently sampled.Find the probability that fewer than half of those sampled currently have access to on-line service. (A) 1,000 (B) .998 (C)994 (D).999

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