Chapter 18: Inferences about Means

Suppose I want to test whether​ students' textbook costs for this semester are higher on average than the average cost of​ $450 in 2000. What would be an appropriate alternative​ hypothesis? Choose the correct answer below. A. μ ≠450 B. μ >450 C. μ <450 D. x overbar >450

B. μ >450

A student on the track team wants to test whether her times to run a mile are different after a new training regimen.​ Previously, her average time to run a mile was 8 minutes. Which is an appropriate alternative​ hypothesis? Choose the correct answer below. A. μ >8 B. μ<8 C. μ ≠8 D. x overbar <8

C. μ ≠8

Suppose we are making a​ 95% confidence interval for the population mean from a sample of size 15. What number of degrees of freedom should we​ use? a. 14 b. 16 c. 15 d. there is not enough information given to find out

a. 14

Which of the following statements is true about the family of t distributions? a. t distributions are symmetric and unimodal b. t distributions have fatter tails and narrower centers than Normal models c. As the degrees of freedom increase, the t distributions approach the Normal distribution

all are true

Suppose we construct a​ 90% confidence interval for a mean. This is equivalent to a​ two-tailed hypothesis test with​ _______ level of significance. a. 5% b. 10% c. 1% d. 20%

b. 10%

Which of the following is not a condition to check to estimate the mean of a​ population? Choose the correct answer below. A. The sample is no more than​ 10% of the population. B. Data are randomly gathered. C. There are at least 10 successes and 10 failures in the sample. Your answer is correct. D. The data come from a population that is unimodal and symmetric.

c. There are at least 10 successes and 10 failures in the sample

On a final project in an introductory statistics​ class, a student reports a​ 95% confidence interval for the average cost of a haircut to be​ ($5.50,$65.00). What is the correct interpretation of this confidence​ interval? a. 95% of the sample falls between these two values. b. There is 95% confidence that the sample mean is between these two values c. There is 95% confidence that the population mean is between these two numbers

c. There is 95% confidence that the population mean is between these two numbers

Suppose we want to estimate the proportion of defective items produced by a manufacturing process. Could we use the methods of this chapter to answer this​ question? yes/ no

no