## MATH 399N Week 7 MyStatLab Quiz

**1. Question:** The time spent (in days) waiting fora kidney transplant tor people ages 35-49 can be approximiated by the normal distribution, as shown in the figure to the right.

(a) What waiting time represents the 95th percentile?

(b) What waiting time represents the first quartile?

**2. Question:** A researcher wishes to estimate, with 90% confidence, the population proportion of adults who are confident with their country’s banking system. His estimate must be accurate within 3% of the population proportion.

(a) No preliminary estimate is available. Find the minimum sample size needed.

(b) Find the minimum sample size needed, using a prior study that found that 36% of the respondents said they are confident with their country’s banking system.

(c) Compare the results from parts (a) and (b).

**3. Question:** The time spent (in days) waiting for a kidney transplant for people ages 35-49 can be

approximiated by the normal distribution, as shown in the figure to the right.

(a) What waiting time represents the 90th percentile?

(b) What waiting time represents the first quartile?

**4. Question:** A manufacturer claims that the life span of its tires is 47,000 miles. You work for a consumer protection agency and you are testing these tires. Assume the life spans of the tires are normally … You select 100 tires at random and test them. The mean life span is 46,894 miles. Assume 0″= 800. Complete parts (a) through (c).

**5. Question:** Construct the confidence interval for the population mean Il.

c = 0.98, x = 15.3, 0″= 10.0, and n = 90

**6. Question:** Find the probability and interpret the results. If convenient, use technology to find the probability. During a certain week the mean price of gasoline was $2.702 per gallon. A random sample of 32 gas stations is … from this population. What is the probability that the mean price for the sample was between $2.677 and $2.716 that week? Assume CJ= $0.05.

**7. Question:** In a random sample of 55 refrigerators, the mean repair cost was $126.00 and the population standard deviation is $15.20. Construct a 95% confidence interval for the population mean repair cost. Interpret the results.

**8. Question:** The table to the right shows the results of a survey in which 400 adults from the East, 400 adults from the South, 400 adults from the Midwest, and 400 adults from the West were asked if traffic congestion is a serious problem. Complete parts (a) and (b).

**9. Question:** People were polled on how many books they read the previous year. How many subjects are needed to estimate the number of books read the previous year within one book with 99% confidence? Initial survey results indicate that C1 =16.5 books.

**10. Question:** Assume a member is selected at random from the population represented by the graph. …. at random is from the shaded area of the graph. Assume the variable x is normally distributed.

**11. Question:** A population has a mean ~ =79 and a standard deviation 0′ =6. Find the mean and standard deviation of a sampling distribution of sample means with sample size n = 36.

## STATUS

**12. Question:** In a survey of a group of men, the heights in the 20-29 age group were normally distributed, with a mean of 67.7 inches and a standard deviation of 4.0 inches. A study participant is randomly … Complete parts (a) through (d) below.

**13. Question:** In a survey of 2785 adults, 1499 say they have started paying bills online in the last year. Construct a 99% confidence interval for the population proportion. Interpret the results.

**14. Question:** The total cholesterol levels of a sample of men aged 35-44 are normally distributed with a mean of 225 milligrams per deciliter and a standard deviation of 38.3 milligrams per deciliter.

(a) What percent of the men have a total cholesterol level less than 238 milligrams per deciliter of blood?

(b) If 249 men in the 35-44 age group are randomly …, about how many would you expect to have a total cholesterol level greater than 261 milligrams per deciliter of blood?

**15. Question:** Assume the random variable x is normally distributed with mean 1.1 = 83 and standard deviation a = 5. Find the indicated probability. P(x < 80)