The manager of a department store is thinking about establishing a new billing system for the store's credit customers. She determines that the new system will be cost-effective only if the mean monthly account is more than $170. A random sample of 400 monthly accounts is drawn, for which the sample mean is $178. The manager knows that the accounts are approximately normally distributed with a standard deviation of $65. Can the manager conclude from this that the new system will be cost-effective at 10% significance level?

Researchers want to compare the relative effectiveness of two popular diets. They randomly assign each of 400 volunteers to one of two Groups: A & B.  There are 200 volunteers in each group. Group A spends 6 months on Diet A. Group B spends 6 months on Diet B.   At the beginning of the study, the difference in average weight between the two groups was negligible. After the study, the Group A had lost on average 7.8 pounds with a standard deviation of 13.4 pounds, while the Group B had lost on average 5.3 pounds with a standard deviation of 14.8 pounds. Determine the z-score/test statistic for a two-tailed test with significance level α = 0.05 , accurate to 2 decimal places.

A personnel psychologist has to decide which of three employees to place in a particular job that requires a high level of coordination. All three employees have taken tests of coordination, but each took a different test. Employee A scored 15 on a test with a mean of 10 and a standard deviation of 2; Employee B scored 350 on a test with a mean of 300 and a standard deviation of 40; and Employee C scored 108 on a test with a mean of 100 and a standard deviation of 16. (On all three tests, higher scores mean greater coordination.) Which employee has the best coordination?   (hint: convert raw scores to z scores and compare)   Select one: a. Employee A b. Employee B c. Employee C Clear my choice

Lucille, Rocio, and Cristina are all taking College Mathematics but from different professors. They all recently took a statistics exam and the exam scores were normally distributed in each of their classes. • Lucille's class had an average grade of 78 and the standard deviation was 7. Lucille earned 83.95 on the exam. • Rocio's class had an average grade of 82 and the standard deviation was 3. Rocio earned 86.5 on the exam. • Cristina's class had an average grade of 76 and the standard deviation was 4. Cristina earmed 82.8 on the exam. Since some professors give harder exams than others, these students decided to use statistics to figure out who did the best on their exam. Use the Cumulative Z-Score Table to answer the following questions. Write your answers as a percent with two decimal places. Hint • Lucille's score places her above % of her class. • Rocio's score places her above % of her class. • Cristina's score places her above % of her class.

Two groups of students took the same test. Group A is having a mean of 60 marks and a standard deviation of 5 markS. Group B is having a mean of 60 marks and a standard deviation of 10 marks. Which of the statements below is correct? A. Group A students have a wider spread in performance than that in group B B. Group B students have a wider spread in performance than that in group A C. Group A students have the same spread in performance than that in group B D. None of the above A

Suppose that you are designing an instrument panel for a large industrial machine. The machine requires the person using it to reach 2 feet from a particular position. The reach from this position for adult women is known to have a mean of 2.7 feet with a standard deviation of 0.5. The reach for adult men is known to have a mean of 3.1 feet with a standard deviation of 0.7. Both women's and men's reach from this position is normally distributed. If this design is implemented, (a) what percentage of women will not be able to work on this instrument panel? (b) What percentage of men will not be able to work on this instrument panel? (c) Explain your answers to a person who has never had a course in statistics. Click here to view page 1 of the table. Click here to view page 2 of the table. Click here to view page 3 of the table. Click here to view page 4 of the table.

Risk taking is an important part of investing. In order to make suitable investment decisions on behalf of their customers, portfolio managers give a questionnaire to new customers to measure their desire to take financial risks. The scores on the questionnaire are approximately normally distributed with a mean of  49  and a standard deviation of  16 . The customers with scores in the bottom  15%  are described as "risk averse." What is the questionnaire score that separates customers who are considered risk averse from those who are not? Carry your intermediate computations to at least four decimal places. Round your answer to one decimal place.