A large population has a distribution that is fairly uniform with a mean of 80 and a standard deviation of 12. If all possible samples of size 36 are taken, which of the following best describes the distribution of sample means? (A) The distribution will also be uniform with a mean of 80 and a standard deviation of 12. (B) The distribution will be approximately normal with a mean of 80 and a standard deviation of 12. (C) The distribution will be symmetric but not approximately normal, with a mean of 80 and a standard deviation of 12. (D) The shape of the distribution will be unknown, but it will have a mean of 80 and a standard deviation of 2. (E) The distribution will be approximately normal with a mean of 80 and a standard deviation of 2.

Two chemical companies can supply a raw material. The concentration of a particular element in this material is important. The mean concentration for both suppliers is the same, but you suspect that the variability in concentration may differ for the two companies. The standard deviation of concentration in a random sample of n₁ = 10 batches produced by company 1 is s₁ = 4.7 grams per liter, and for company 2, a random sample of n₂ = 16 batches yield s₂ = 5.8 grams per liter. Is there sufficient evidence to conclude that the two populations variances differ? Use a = 0.05. a. Because 0.321 < 0.657 <3.77, fail to reject the null hypothesis b. Because 0.265 < 0.657 <3.12, fail to reject the null hypothesis c. Because 0.386 < 0.657 <3.01, fail to reject the null hypothesis d. None among the choices

Suppose that Melanie is a researcher who wishes to estimate the mean birthweight of full-term babies in her hospital. What is the minimum number of babies should she sample if she wishes to be at least 90% confident that the mean birthweight of the sample is within 225 grams of the the mean birthweight of all babies? Assume that the distribution of birthweights at her hospital is normal with a standard deviation of 600 g.

he average amount of time boys and girls spend playing sports each week is believed to be the same. A sample of equal size n is taken from boys and girls , the mean of the boys is 29 hours with standard deviation 4 hours and the mean of the girls is 27 hours with standard deviation 3 hours Both populations have a normal distribution. The calculated value is 1.2 n =