Adrian claims that his new training methods have improved his batting average. Before starting his new regimen, he was batting 0.220 in a random sample of 50 bats. For a random sample of 24 at-bats since changing his training technique, his batting average is 0.375. Determine if there is sufficient evidence to say that his batting average has improved at the 0.10 (10%) level of significance.

Citrus Rental is a popular car rental agency that has a history of having too few cars available, so that its available cars are overdriven. The mean monthly mileage over the years for Citrus cars has been about 1500 miles per month. Recently, though, Citrus purchased thousands of new cars, and the company claims that the average mileage of its cars is now less than in the past. To test this, a random sample of 11 recent mileages of Citrus cars was taken. The mean of these 11 mileages was 1332 miles per month, and the standard deviation was 232 miles per month. Assume that the population of recent monthly mileages of Citrus cars is normally distributed. At the 0.05 level of significance, can it be concluded that the mean recent monthly mileage, u, of Citrus cars is less than 1500 miles per month? Perform a one-tailed test. Then complete the parts below. Carry your intermediate computations to three or more decimal places and round your answers as specified in the table. (If necessary,…

A dietitian wishes to see if a person's cholesterol level will change if the diet is supplemented by a certain mineral. Seven subjects were pretested and then took the mineral supplement for a six-week period. The results are shown below in the table. Use a paired samples t-chart at a = 0.01 significance level to see difference (Before - After) between the cholesterol levels. State the hypotheses and conclusion. Also, conduct a 99% confidence interval. Subject 1 Before 210 After 190 2 205 170 3 208 210 4 192 188 5 178 173 6 244 228 7 211 198

In 1965, about 44% of the u.s. adult population had never smoked cigarettes. A national health survey of 1360 u.s adults(selected randomly) during 2020 revealed that 626 had never smoked cigarettes. Using a=0.05, test whether there has been a change since 1965 in the proportion of u.s. adults that have never smoked cigarettes. State the hypothesis, list and check the conditions, calculate the test statistic, find the p-value, and make a conclusion in a complete sentence related to the scenario

According to a survey conducted by the Association for Dressing and Sauces, 85% of American adults eat salad at least once a week. A nutritionist suspect that the percentage is higher that this. She conducts a survey of 200 American adults an finds that 171 of them eat salad at least once a week. Conduct the appropriate test that addresses the nutritionist's suspicions. Use the a = 0.1 level of significance. What is the test statistic? t-score population parameter Z-Score standard deviation

You are the Director of Ticket Sales for the Kansas City Royals.  Over the past 10 years, average attendance has dipped, thus the ownership group is considering improvements to the stadium to attract younger fans.  From the period since Kauffman Stadium opened (April 1973) through October 2012, the average game attendance was 22,655.  For the 2019 season—82 home games—the average attendance was 22,402 with a sample standard deviation of 899.  Before the ownership group commits to $275M in stadium upgrades, they ask you for statistical evidence that attendance has decreased.      Why is a hypothesis test a better statistical approach than a confidence interval to base your response to the ownership group?  Is the appropriate hypothesis test a left, right, or two-tailed test?  State the null and alternative hypotheses for the appropriate test.  You choose to conduct the test at the .01 level of significance (having an associated critical value of +/- 2.37) and determine the test…

A publisher reports that 69 % of their readers own a particular make of car. A marketing executive wants to test the claim that the percentage is actually under the reported percentage. A random sample of 200 found that 60% of the readers owned a particular make of car. Is there sufficient evidence at the 0.10 level to support the executive's claim? Step 5 of 7: Identify the value of the level of significance.

A statistician changes her level of significance from .001 to .05.  What impact will this change have on her risk of making a Type I and Type II error?  Is the change in the level of significance a good decision?  Why or why not?

The average spent nationally on Christmas gifts in 2020 was reported to be $650 per person. Below is a random sample of gift givers from Iowa and what they spent in 2020.    Is there sufficient evidence to conclude that Iowans spend less than the national average?         Estimate the average amount spent by Iowans on Christmas gifts in 2020 with a 90%-CI.     700 450 400 525 550 550 600 575 650 625 500