91影视

Marketing companies have collected data implying that teenage girls use more ring tones on their cellular phones than

teenage boys do. In one particular study of 40 randomly chosen teenage girls and boys (20 of each) with cellular phones,

the mean number of ring tones for the girls was 3.2 with a standard deviation of 1.5. The mean for the boys was 1.7 with

a standard deviation of 0.8. Conduct a hypothesis test to determine if the means are approximately the same or if the girls鈥�

mean is higher than the boys鈥� mean.

83. Using the data from Lap 1 only, conduct a hypothesis test to determine if the mean time for completing a lap in races is the same as it is in practices.

Repeat the test in Exercise 10.83, but this time combine the data from Laps 1 and 5.

In two to three complete sentences, explain in detail how you might use Terri Vogel鈥檚 data to answer the following

question. 鈥淒oes Terri Vogel drive faster in races than she does in practices?鈥�

86. In two to three complete sentences, explain in detail how you might use Terri Vogel's data to answer the following question. "Does Terri Vogel drive faster in races than she does in practices?"
Use the following information to answer the next two exercises. The Eastern and Western Major League Soccer conferences have a new Reserve Division that allows new players to develop their skills. Data for a randomly picked date showed the following annual goals.

Conduct $a$ hypothesis test to answer the next two exercises.
87. The exact distribution for the hypothesis test is:
a. the normal distribution
b. the Student's $t$-distribution
c. the uniform distribution
d. the exponential distribution

88. If the level of significance is $0.05$, the conclusion is:
a. There is sufficient evidence to conclude that the $\mathbf{W}$Division teams score fewer goals, on average, than the $\mathbf{E}$ teams
b. There is insufficient evidence to conclude that the $\mathbf{W}$ Division teams score more goals, on average, than the $\mathbf{E}$ teams.
c. There is insufficient evidence to conclude that the $\mathbf{W}$ teams score fewer goals, on average, than the $\mathbf{E}$ teams score.
d. Unable to determine

89. Suppose a statistics instructor believes that there is no significant difference between the mean class scores of statistics day students on Exam 2 and statistics night students on Exam 2. She takes random samples from each of the populations. The mean and standard deviation for 35 statistics day students were 75.86 and 16.91. The mean and standard deviation for 37 statistics night students were 75.41 and 19.73. The "day" subscript refers to the statistics day students. The "night" subscript refers to the statistics night students. A concluding statement is:
a. There is sufficient evidence to conclude that statistics night students' mean on Exam 2 is better than the statistics day students' mean on Exam 2.
b. There is insufficient evidence to conclude that the statistics day students' mean on Exam 2 is better than the statistics night students' mean on Exam 2.
c. There is insufficient evidence to conclude that there is a significant difference between the means of the statistics day students and night students on Exam 2.
d. There is sufficient evidence to conclude that there is a significant difference between the means of the statistics day students and night students on Exam 2.

In a random sample of 100 forests in the United States, 56 were coniferous or contained conifers. In a random sample of 80 forests in Mexico, 40 were coniferous or contained conifers. Is the proportion of conifers in the United States statistically more than the proportion of conifers in Mexico?

90. Researchers interviewed street prostitutes in Canada and the United States. The mean age of the 100 Canadian prostitutes upon entering prostitution was 18 with a standard deviation of six. The mean age of the 130 United States prostitutes upon entering prostitution was 20 with a standard deviation of eight. Is the mean age of entering prostitution in Canada lower than the mean age in the United States? Test at a $1\%$ significance level.