9 STAT QUESTIONS FOR STRONG HEART ONLY

1. A sample of size n=38 drawn from a population with σ=9.9 has x¯=18.1. Find a 93% confidence interval for the population mean by completing each of the following in turn. Round all your answers to the nearest hundredth.

x¯=

c=

zc=

E=

Confidence interval is ( , )

2.

For the picture above, which shows the standard normal curve with critical values marked, if c=0.85, then zc= . (Round your answer to four decimal places.)

3. The systolic blood pressure (SBP) of a certain population is normally distributed with standard deviation 7 mmHg. A sample of 23 members of this population was found to have an average SBP of 118 mmHg. Find a 93% confidence interval for the population mean. Round the endpoints to the nearest integer.

Confidence interval is ( , )

4. The average starting salaries for 52 graduates with a certain major was $40377. The standard deviation for all graduates with that major was $8631. Give the 93% confidence interval for the population mean. Round the endpoints to the nearest dollar, and do not put commas in your numbers.

Confidence interval: ( , )

5. The diameter of the twelve-penny common nails made by ’Snails!, Inc., is normally distributed with standard deviation 0.004 in. A sample of 29 such nails was found to have a mean diameter of 0.127 in. Find a 92% confidence interval for the mean diameter of all such nails. Round the endpoints to five decimal places.

Confidence interval is ( , )

6. If 280 confidence intervals, each having a 97% level of confidence, were computed for a population mean μ, about how many of the intervals can be expected to contain μ? (Your answer will be an integer, of course.)

7. What quantity is added to and subtracted from a sample mean to construct a confidence interval?

A. The sample standard deviation
B. The standard error
C. The population standard deviation
D. The margin of error
E. The population mean

8.A z-confidence interval is computed for the mean of a population with standard deviation σ. Answer all of the following questions by making the appropriate choice from the popup list.

(i)	Assuming that no other change is made, if the interval is recomputed using a higher level of confidence, then the resulting interval will be ? narrower wider than the original interval.

(ii)	Assuming that no other change is made, if the interval is recomputed using a smaller sample, then the resulting interval will be ? wider narrower than the original interval.

(iii)

Suppose that it is found that the population standard deviation is actually less than σ. Assuming that no other change is made, if the interval is recomputed using the new value for the standard deviation, then the resulting interval will be ? narrower wider than the original interval.

9. If 300 confidence intervals, each having a level of confidence of 97%, were computed for a population mean μ, approximately how many of the intervals would be expected to contain μ? (Round your answer to the nearest integer.)