Past experience indicates that the time required for high school seniors to complete a standardized test is a normal random variable with a mean of 35 minutes. If a random sample of 20 high school seniors took an average of 33.1 minutes to complete this test with a standard deviation of 4.3 minutes, test the hypothesis, at the 0.05 level of significance, that μ = 35 minutes against the alternative that μ < 35 minutes.

Data provided by the National Association of College Employers indicated that the average starting salary for graduates with a Bachelors Degree in Accounting was $37,000 in 2008. In June 2010 a sample of 48 graduating accounting majors provided a sample average starting salary of $38,100, with a sample standard deviation of $5200. Conduct a hypothesis test to determine if it can be assumed that accounting graduates in 2010 had higher average salaries than graduates in 2008, using α = .05.

The manager of a computer retails store is concerned that his suppliers have been giving him laptop computers with lower than average quality. His research shows that replacement times for the model laptop of concern are normally distributed with a mean of 3.3 years and a standard deviation of 0.4 years. He then randomly selects records on 25 laptops sold in the past and finds that the mean replacement time is 3.2 years.Assuming that the laptop replacement times have a mean of 3.3 years and a standard deviation of 0.4 years, find the probability that 25 randomly selected laptops will have a mean replacement time of 3.2 years or less.P(M < 3.2 years) = Enter your answer as a number accurate to 4 decimal places. NOTE: Answers obtained using exact z-scores or z-scores rounded to 3 decimal places are accepted.Based on the result above, does it appear that the computer store has been given laptops of lower than average quality? No. The probability of obtaining this data is high enough…

5.37 Dental anxiety study. To gauge their fear of going to a den- tist, a random sample of adults completed the Modified Dental Anxiety Scale questionnaire (BMC Oral Health, Vol. 9, 2009). Scores on the scale range from zero (no anx- iety) to 25 (extreme anxiety). The mean score was 11 and the standard deviation was 4. Assume that the distribution of all scores on the Modified Dental Anxiety Scale is ap- proximately normal with µ = 11 and o = 4. a. Suppose you score a 10 on the Modified Dental Anxiety Scale. Find the z-value for your score. b. Find the probability that someone scores between 10 and 15 on the Modified Dental Anxiety Scale. c. Find the probability that someone scores above 20 on the Modified Dental Anxiety Scale.

A class survey in a large class for first‑year college students asked, “About how many hours do you study during a typical week?” The mean response of the 463 students was x= 13.7 hours. Suppose that we know that the study time follows a Normal distribution with standard deviation o= 7.4 hours in the population of all first‑year students at this university. Regard these students as an SRS from the population of all first‑year students at this university. Does the study give good evidence that students claim to study more than 13 hours per week on the average? (b) What is the value of the test statistic  ? (Enter your answer rounded to two decimal places.) =

A researcher claims that the average life span of mice can be extended when the calories in their diet are reduced by approximately 40% from the time they are weaned. The restricted diets are enriched to normal levels by vitamins and protein. Suppose that a sample of 10 mice is fed a normal diet and has anaverage life span of 32.1 months with a standard deviation of 3.2 months, while a sample of 15 mice is fed the restricted diet and has an average life span of 37.6 months with a standard deviation of 2.8 months. Assume the distributions of life spans for the regular and restricted diets are approximately normal withequal variance.(a) State the appropriate hypotheses to test the researcher’s claim.(b) Conduct the test at the 0.05 level of significance. What do you conclude?

A UCLA researcher claims that the average life span of mice can be extended by as much as 8 months when the calories in their diet are reduced by approximately 40% from the time they are weaned. The restricted diets are enriched to normal levels by vitamins and protein. Suppose that a random sample of 10 mice is fed a normal diet and has an average life span of 32.1 months with a standard deviation of 3.2 months, while a random sample of 15 mice is fed the restricted diet and has an average life span of 37.6 months with a standard deviation of 2.8 months. Test the hypothesis, at the 0.05 level of significance, that the average life span of mice on this restricted diet is increased by 8 months against the alternative that the increase is less than 8 months. Assume the distributions of life spans for the regular and restricted diets are approximately normal with equal variances. Do not use t-test statistic.