Suppose that memory for unrelated words is distributed normally with a mean of µ = 60 with a standard deviation of σ = 20. A random sample is selected from this population.  After a treatment is administered to the individuals in the sample, a memory test that measures memory for unrelated words is administered, the sample mean is found to be M = 55. If the sample consists of n = 25 scores, can we conclude that the treatment has a significant effect? Use a two-tailed test with α=.01 a. The alternative hypothesis in words is: b. The null hypothesis in symbols is c. The critical z values are d. The z-score statistic is: e. Final decision?

An ecologist is studying the impact of local polluted waters on the growth of alligators. The length of adult male alligators typically follows a normal distribution with a standard deviation of 2 feet. The ecologist wants to estimate the mean length of this population of alligators. Suppose she samples n alligators at random and uses the sample mean, X to as an estimator for u. a. What is the bias and variance of the estimator? (Note, these may be a function of n.) b. If n = 4, what is the probability that the estimator is within one foot of the true mean? (I.e. find P(|X – µ| < 1). c. What sample size, n, is required for the estimator to be within one foot of the true mean with 95% probability? (I.e. find the value of n that satisfies P(|X – µ| < 1) = 0.95.) d. Suppose the ecologist ends up sampling n = 9 alligators and calculates a sample mean of ī = 10.4 feet. Construct a 95% confidence interval for the population mean. e. Give an interpretation for the interval obtained in (d).

A scientist is worried about a new disease being spread by mosquitoes in an area. The scientist captures a random sample of 137 mosquitoes from the area and tests them to find out whether they carry the disease. In this sample, 22 of the mosquitoes were carrying the disease. Using this information, the scientist uses 100 simulations of additional samples with the same proportion of disease-carrying mosquitoes from the sample to determine that the standard deviation for the proportion of mosquitoes carrying the disease is approximately 0.029. What is the margin of error for the estimated proportion of mosquitoes in the area that carry the disease?

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  1550  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  19  recent mileages of Citrus cars was taken. The mean of these  19  mileages was  1532  miles per month, and the standard deviation was  208  miles per month.   Assume that the population of recent monthly mileages of Citrus cars is normally distributed. At the  0.1  level of significance, can it be concluded that the mean recent monthly mileage,  μ , of Citrus cars is less than  1550  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…

The yield per tract in a certain region of farmland is known to have a populationstandard deviation of 13 bushels. Using the old seed variety, the population mean yield μwas 39 bushels. A farmer tests a new seed variety on a random sample of 36 tracts, andfinds a sample mean yield of 45.2 bushels. Is the population mean yield using the newseed variety different from 39? Use α= 0.10.a. State the null hypothesis . __________________State the alternative hypothesis.____________________b. Find the test statistic. _____ c. Find the P-value for the test. _____________

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 1550 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 15 recent mileages of Citrus cars was taken. The mean of these 15 mileages was 1517 miles per month, and the standard deviation was 201 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, μ, of Citrus cars is less than 1550 miles per month?   Perform a one-tailed test. Then complete the parts below.

In the year 2033, Sarai Patterson is a leading traveling nurse. Sarai is interested in reducing the mean recovery time for patients after experiencing a serious injury (assume recovery times are normally distributed). Suppose the mean recovery time is presently 8.6 months. Sarai takes a random sample of 46 patients that have experienced serious injury to participate in a new treatment program and finds the sample mean is 8.1 months and a sample standard deviation of 1.2 months. Using α = 0.05, answer the following questions. a) What is the setup for your null and alternative hypothesis? b) What is the value of the test statistic? c) What is/are the critical value(s)?

A researcher wonders whether the recession has changed variability in family size in his city. Before the recession, the mean was 3.7 and the standard deviation was 1.76. The researcher randomly selects 41 families from a population that is normally distributed. His sample has a mean of 3.1 and a standard deviation of 1.45. Test the claim that the standard deviation in size has changed at the αα=.05 significance level.

Agricultural scientists are testing a new chicken feed to see whether it increases the number of eggs laid. The scientists divided a flock in half and gave half of the chickens the new feed, while the other half were given a regular feed. The eggs laid in a one-year period for a random sample of 10 chickens using the new feed and 10 chickens using the regular feed are recorded. Assume that the population standard deviation of number of eggs laid is 12 eggs per year for both groups and that the number of eggs laid per year is normally distributed. Let the chickens given the new feed be the first sample, and let the chickens given the regular feed be the second sample. The scientists conduct a two-mean hypothesis test at the 0.05 level of significance to test if there is evidence that the new feed increases the number of eggs laid.   (a)  Which answer choice shows the correct null and alternative hypotheses for this test? Select the correct answer below:   H0:μ1=μ2;…

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 1550 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 13 recent mileages of Citrus cars was taken. The mean of these 13 mileages was 1425 miles per month, and the standard deviation was 209 miles per month. Assume that the population of recent monthly mileages of Citrus cars is normally distributed. At the 0.10 level of significance, can it be concluded that the mean recent monthly mileage, μ, of Citrus cars is less than 1550 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,…