# STATS

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12- The number of cars sold annually by used car salespeople is normally distributed with a standard deviation
of 19.22. A random sample of salespeople was taken and the number of cars each sold is listed her.
79 43 58 66 101 63 79 33
58 71 60 101 74 55 88
The 95% confidence interval estimate of the population mean is
(1) (58.873; 78.327)
(2) (66.099; 71.111)
(3) (686.000; 255.542)
(4) (68.600; 78.327)
(5) (588.730; 783.270)

13-A random sample of 40 men drank an average of 20 cups of coffee per week during examination final,
with the population standard deviation equal to 6 cups. A lower limit of an approximate 95% confidence
interval the population average cup of coffee is
(1) 20.000
(2) 21.859
(3) 19.708
(4) 18.141
(5) 19.051

14-In a random sample of 500 students, 80% say they have a part-time job. An approximate 95% confidence
interval for the proportion of students with part-time jobs is:
(1) (0.758; 0.842)
(2) (0.765; 0.835)
(3) (0.770; 0.830)
(4) (0.800; 0.835)
(5) (0.782; 0.819)

15-Which statement is incorrect?
(1) A null hypothesis is a statement about the value of a population parameter; it is put up for testing in
the face of numerical evidence.
(2) An alternative hypothesis is an assertion that holds if the null hypothesis is false.
(3) A one-tail test is one in which a null hypothesis can be rejected by an extreme result in one direction
only.
(4) A two-tail test is one in which a null hypothesis can be rejected by an extreme result occurring in either
direction.
(5) A p–value greater than 0.05 means that the null hypothesis can be rejected at the 5% significance level.

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