A sample of 9 production managers with over 15 years of experience has an average salary of $71,000 and a sample standard deviation of $18,000. what sample size would be needed to ensure that we could estimate the true mean salary of all production managers with more than 15 years experience within $4200 if we wish to be 95% confident?

Fran is training for her first marathon, and she wants to know if there is a significant difference between the mean number of miles run each week by group runners and individual runners who are training for marathons. She interviews 42 randomly selected people who train in groups and finds that they run a mean of 47.1 miles per week. Assume that the population standard deviation for group runners is known to be 4.4 miles per week. She also interviews a random sample of 47 people who train on their own and finds that they run a mean of 48.5 miles per week. Assume that the population standard deviation for people who run by themselves is 1.8 miles per week. Test the claim at the 0.01 level of significance. Let group runners training for marathons be Population 1 and let individual runners training for marathons be Population 2.   Step 2 of 3 :   Compute the value of the test statistic. Round your answer to two decimal places.

A study shows that Michigan teachers have measures of job dissatisfaction that are normally distributed with a mean of 3.80 and standard deviation of 0.95. If subjects with scores above 4.0 are to be given more tests, what percentage will fall into that category?

Humerus bones from the same species of animal have approximately the same length-to-width ratios. It is known that Species A has a mean ratio of 5.9. Suppose that 100 fossil humerus bones were unearthed at a site where Species A is known to have flourished. (We assume that all bones are from the same species.) The length-to-width ratios of these bones have a sample mean 5.6 and sample standard deviation 0.25.   Can we conclude that the mean ratio of these bones is significantly smaller than those of Species A? Test with a 0.01 significance level.   What is the standard error?

In a sample of 351 gamers between the ages of 16-25, the mean number of hours spent gaming per week was 42.5 hours. In a sample of 269 gamers between the ages of 26-40, the mean number of hours spent gaming per week was 43.8 hours. If the population standard deviation for the mean number of hours spent gaming per week is 9.5 for the age group 16-25 and 10.7 for the age group 26-40, test the claim that gamers between the ages of 16-25 spend less time gaming per week than gamers between the ages of 26-40. Assume α=0.03.      Let population 1 be gamers in the age group 16-25 and population 2 be gamers in the age group 26-40. Round the test statistic to two decimal places, and round the p-value to four decimal places.   The test statistic is . The p-value is . Should the null hypothesis be rejected?

1) A​ half-century ago, the mean height of women in a particular country in their 20s was 63.7 inches. Assume that the heights of today's women in their 20s are approximately normally distributed with a standard deviation of 2.31 inches. If the mean height today is the same as that of a​ half-century ago, what percentage of all samples of 26 of today's women in their 20s have mean heights of at least 65.04 ​inches?