# UMUC STAT200 week 6 homework

Question

Lane Chap. 11

18. You choose an alpha level of .01 and then analyze your data.

a. What is the probability that you will make a Type I error given that the null hypothesis is true?

b. What is the probability that you will make a Type I error given that the null hypothesis is false?

Lane Chap.12

13. You are conducting a study to see if students do better when they study all at once or in intervals. One group of 12 participants took a test after studying for one hour continuously. The other group of 12 participants took a test after studying for three twenty minute sessions. The ?rst group had a mean score of 75 and a variance of 120. The second group had a mean score of 86 and a variance of 100.

a. What is the calculated t value? Are the mean test scores of these two groups signi?cantly different at the .05 level?

b. What would the t value be if there were only 6 participants in each group? Would the scores be signi?cant at the .05 level?

Illowsky Chap.9

65.Previously,anorganizationreportedthatteenagersspent4.5hoursperweek,onaverage, on the phone.Theorganization thinks that, currently, the mean is higher. Fifteen randomly chosen teenagers were asked how many hours per week they spend on the phone. The sample mean was 4.75 hours with a sample standard deviation of 2.0. Conduct a hypothesis test. The null and alternative hypotheses are:

a. Ho: x ¯ = 4.5,Ha : x ¯ > 4.5

b. Ho:?? 4.5,Ha:? 4.75

d. Ho:?= 4.5,Ha:?> 4.5

71.Previously,anorganizationreportedthatteenagersspent4.5hoursperweek,onaverage,onthephone.Theorganization thinks that, currently, the mean is higher. Fifteen randomly chosen teenagers were asked how many hours per week they spend on the phone. The sample mean was 4.75 hours with a sample standard deviation of 2.0. Conduct a hypothesis test, the Type I error is:

a. to conclude that the current mean hours per week is higher than 4.5, when in fact, it is higher

b. to conclude that the current mean hours per week is higher than 4.5, when in fact, it is the same

c. to conclude that the mean hours per week currently is 4.5, when in fact, it is higher

d. to conclude that the mean hours per week currently is no higher than 4.5, when in fact, it is not higher

77. AnarticleintheSanJoseMercuryNewsstatedthatstudentsintheCaliforniastateuniversitysystemtake4.5years,on average, to finish their undergraduate degrees. Suppose you believe that the mean time is longer. You conduct a survey of 49 students and obtain a sample mean of 5.1 with a sample standard deviation of 1.2. Do the data support your claim at the 1% level?

Illowsky Chap.10

80. At Rachel’s 11th birthday party, eight girls were timed to see how long (in seconds) they could hold their breath in a relaxed position. After a two-minute rest, they timed themselves while jumping. The girls thought that the mean difference between their jumping and relaxed times would be zero. Test their hypothesis.

Relaxed time (seconds)

Jumping time (seconds)

26

21

47

40

30

28

22

21

Relaxed time (seconds)

Jumping time (seconds)

23

25

45

43

37

35

29

32

91. A powder diet is tested on 49 people, and a liquid diet is tested on 36 different people. Of interest is whether the liquid diet yields a higher mean weight loss than the powder diet. The powder diet group had a mean weight loss of 42 pounds withastandarddeviationof12pounds.Theliquiddiet grouphadameanweightlossof45poundswithastandarddeviation of 14 pounds.

120. A golf instructor is interested in determining if her new technique for improving players’ golf scores is effective. She takesfournewstudents.Sherecordstheir18-holescoresbeforelearningthetechniqueandthenafterhavingtakenherclass. She conducts a hypothesis test. The data are as follows.

Player 1

Player 2

Player 3

Player 4

Mean score before class

83

78

93

87

Mean score after class

80

80

86

86

The correct decision is:

a. RejectH0.

b. Do not reject the H0.

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