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Chapter 10: Q.70 (page 659)
The two-sample t statistic for the road rage study (male mean minus female mean) is . The P-value for testing the hypotheses from the previous exercise satisfies
(a) .
(b) .
(c) .
(d) .
(e) .
The correct option is (b).
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A sample survey interviews SRSs of female college students and male college students. Each student is asked whether he or she worked for pay last summer. In all, 410 of the women and 484 of the men say 鈥淵es.鈥� The pooled sample proportion who worked last summer is about
(a)
(b)
(c)
(d)
(e)
48. Did the randomization produce similar groups? First, compare the two groups of birds in the first year. The only difference should be the
chance effect of the random assignment. The study report says: 鈥淚n the experimental year, the degree of synchronization did not differ between
food-supplemented and control females.鈥� For this comparison, the report gives .
(a) What type of statistic (one-sample, paired, or two-sample) is this? Justify your answer.
(b) Explain how this value of t leads to the quoted conclusion.
44. Tropical flowers Different varieties of the tropical flower Heliconia are fertilized by different species of hummingbirds.
Researchers believe that over time, the lengths of the flowers and the forms of the hummingbirds鈥� beaks have evolved to match each other. Here are data on the lengths in millimeters for random samples of two color varieties of the same species of flower on the island of Dominica:
(a) A Fathom dotplot of the data is shown below. Use the graph to answer these questions:
(b) Construct and interpret a 95% confidence interval for the difference in the mean lengths of these two varieties of flowers.
(c) Does the interval support the researchers鈥� belief that the two flower varieties have different average lengths? Explain.
Thirty randomly selected seniors at Council High School were asked to report the age (in years) and mileage of their main vehicles. Here is a scatterplot of the data:
(a) What is the equation of the least-squares regression line? Be sure to define any symbols you use.
(b) Interpret the slope of the least-squares line in the context of this problem. (c) One student reported that her -year-old car had miles on it. Find the residual for this data value. Show your work
Mrs. Woods and Mrs. Bryan are avid vegetable gardeners. They use different fertilizers, and each claims that hers is the best fertilizer to use when growing tomatoes. Both agree to do a study using the weight of their tomatoes as the response variable. They had each planted the same varieties of tomatoes on the same day and fertilized the plants on the same schedule throughout the growing season. At harvest time, they each randomly select tomatoes from their respective gardens and weigh them. After performing a two-sample t-test on the difference in mean weights of tomatoes, they get and . Can the gardener with the larger mean claim that her fertilizer caused her tomatoes to be heavier?
(a) No, because the soil conditions in the two gardens is a potential confounding variable.
(b) No, because there was no replication.
(c) Yes, because a different fertilizer was used on each garden.
(d) Yes, because random samples were taken from each garden.
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