Question

1. Faculty members at a large university have found that over the past several semesters that a cell phone rings in class on average 20 times per semester. A reporter for the school newspaper claims that students are more courteous with their cell phones now than in past semesters,and that the average has decreased. The reporter finds that in a random sample of 19 classes, the average number of times a cell phone rang last semester was 18.3 with a standard deviation of 2.7 calls. Does the evidence support the reporters claim? Perform a complete hypothesis test, using a 5% level of confidence.

2. Assume that when someone is randomly selected there is a 0.6 probability that the selected person believes that honesty is always the best policy.

A) If four people are randomly selected, find the probability that they all believe that honesty is always the best policy

B) If someone is randomly selected, what is the
probability that he or she does *not* believe that honesty
is always the best policy.

Answer #1

1.

H0: Null Hypothesis: 20

HA: Alternative Hypothesis: < 20

SE = s/

= 2.7/ = 0.6194

Test statistic is:

t = ( - )/SE

= (18.3 - 20)/0.6194 = - 2.7446

= 0.05

ndf = 19 - 1 = 18

One Tail - left side test

From Table, critical value of t = - 1.7341

Since the calculated value of t = - 2.7446 is less than critical value of t = - 1.7341, Reject H0.

Conclusion:

The data support the claim that the students are more courteous
with their cell phones now than in past semesters, and that the
average has decreased.

2.

(A) P(All 4 people believe that honesty is always the best
policy) = 0.6^{4} = 0.1296

(B) P(Does not believe that honesty is always the best policy) = 1 - 0.6 = 0.4

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