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Exam 11: Two-Sample Tests of Hypothesis

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Question 41

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When testing the difference between two population means, the degrees of freedom must be computed when

A) the population standard deviations are known and equal.
B) the population means are known.
C) the population standard deviations are assumed unequal and unknown.
D) the population standard deviations are assumed equal but unknown.

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Question 42

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To compare the effect of weather on sales of soft drinks, a soda manufacturer sampled two regions of the country with the following results. Is there a difference in sales between the 2 regions? What is the null hypothesis? _____________________

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Question 43

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In a market test of a new chocolate raspberry coffee, a poll of 400 people from Dobbs Ferry showed 250 preferred the new coffee. In Irvington, 170 out of 350 people preferred the new coffee. To test the hypothesis that there is no difference in preferences between the two villages, what is the alternate hypothesis?

A company is researching the effectiveness of a new web site design to decrease the time to access a website. Five web site users were randomly selected and their times (in seconds) to access the web site with the old and new designs were recorded. The results follow.

A study by a bank compared the average savings of customers who were depositors for three years or less, with those who had been depositors for more than three years. The results of a sample are: If the population standard deviations are unknown and assumed unequal, what are the degrees of freedom?

When independent samples are used to test for differences in the population means with equal population standard deviations, we _______ the variances.

20 randomly selected statistics students were given 15 multiple-choice questions and 15 open-ended questions - all on the same material. The professor was interested in determining which type of questions the students scored higher. This experiment is an example of

When dependent samples are used to test for differences in the means, we pool the sample variances.

A national manufacturer of ball bearings is experimenting with two different processes for producing precision ball bearings. It is important that the diameters be as close as possible to an industry standard. The output from each process is sampled and the average error from the industry standard is calculated. The results are presented below. The researcher is interested in determining whether there is evidence that the two processes yield different average errors. Assume that the population standard deviations are equal. What is the null hypothesis?

If the null hypothesis states that there is no difference between the mean net income of retail stores in Chicago and New York City, then the test is two-tailed.

The net weights (in grams) of a sample of bottles filled by a machine manufactured by Edne, and the net weights of a sample filled by a similar machine manufactured by Orno, Inc., are: Edne: 5, 8, 7, 6, 9 and 7 Orno: 8, 10, 7, 11, 9, 12, 14 and 9 Testing the claim at the 0.05 level that the mean weight of the bottles filled by the Orno machine is greater than the mean weight of the bottles filled by the Edne machine, what is the critical value? Assume equal standard deviations for both samples.

When the standard deviations are equal but unknown, a test for the differences between two population means has n - 1 degrees of freedom.

If samples taken from two populations that are dependent, then a test of ______ differences is applied.

If we are testing for the difference between two population proportions, it is assumed that the two samples are large enough that the binomial distribution can be approximated by _____.

To compare the effect of weather on sales of soft drinks, a soda manufacturer sampled two regions of the country with the following results. Is there a difference in sales between the 2 regions? What is the proportion of sales made in Region A? ______

For a hypothesis comparing two population means, what is the critical value for a one-tailed hypothesis test, using a 5% level of significance level, with both sample sizes equal to 13? The standard deviations for the samples are 5 and 7. Assume the population standard deviations are unequal.

The pooled estimate of the proportion is found by dividing the total number of samples by the total number of successes.

When the population standard deviations are unknown, what is the purpose of pooling the sample variances when testing the difference between two population means? ___________

A recent study focused on the number of times men and women send a Twitter message in a day. The information is summarized below. At the .01 significance level, is there a difference in the mean number of times men and women send a Twitter message in a day? What is the p-value hypothesis test?

For a hypothesis test comparing two population means, the combined degrees of freedom are 24. Which of the following statements about the two sample sizes is NOT true? Assume the population standard deviations are equal.