A recording firm wants the distribution of lengths of cuts on its playlists to have an average of 135 sec and a standard deviation of 2.5 sec so that the radio disc jockeys have plenty of time for commercials within each 5-minute period. The population is normal. A sample of 41 showed a sample mean of 130 and a standard deviation of 5 seconds. Test the claim that the true standard deviation is still 2.5 secs. Use a 5% and a 1% level of significance.

A certain department store is interested in estimating the average amount its credit card customers spent on their first visit. Fifteen credit card accounts were randomly sampled and analyzed with the following results: x=2.525 pesos and s²=20,000 Construct a 95% confidence interval for the average amount its credit card customers spent in the store. A 2,425.00<<2,625.52 B 2,454.45<<2,696.14 2,446.86<<2,603.14 D2,384.86<<2,666.05

Suppose that the distance of fly balls hit to the outfield (in baseball) is normally distributed with a mean of 250 feet and a standard deviation of 44 feet. Let X = distance in feet for a fly ball. Find the 80th percentile of the distribution of fly balls. (Round your answer to one decimal place.)

An environmental researcher took 30 water samples from different areas of a lake. He measured the pH level of each water sample. The standard deviation for the 30 pH levels was about 1.4.What is the best interpretation of the standard deviation? The pH level of a typical water sample was about 1.4 units from the mean on average. The difference between the minimum and maximum pH levels was about 1.4 units. The entire lake had a pH level that was about 1.4 units. The pH level of any given water sample was about 1.4 units from the mean. - this one is wrong

A study reported that the mean concentration of ammonium in water wells in the state of Iowa was 0.71 milligram per liter, and the standard deviation was 1.09 milligrams per liter. Is it possible to determine whether these concentrations are approximately normally distributed. If so, say whether they are normally distributed, and explain how you know. If not, describe the additional information you would need to determine whether they are normally distributed.

A successful basketball player has a height of 6 feet 11 ​inches, or 211 cm. Based on statistics from a data​ set, his height converts to the z score of 5.17. How many standard deviations is his height above the​ mean?

The serum cholesterol levels for men in one age group are normally distributed with a mean of 178.1 and a standard deviation 40.5. All units are in mg/10 mL.  Find the 40th             The annual precipitation for one city is normally distributed with a mean of 26.8 inches and a standard deviation of 3.2 inches. What precipitation amounts will contain 99.7% of the observations?

According to data for a​ population, 3-year-old boys have a mean height of 39 inches and a standard deviation of 2 inches. Assume the distribution is approximately Normal.  Find the percentile measure for a height of 41 inches for a​ 3-year-old boy

Suppose that the mean and standard deviation for vertical jump scores are 40 and 6 cm respectively.  A York student jumps 52 cm on the vertical score.  Translate the student’s jump into a z-score.