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Name: May 1, 2001 Score:

MATH 147

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Quiz 12

(10 pts.)

Problem 1. A county with a large population need to know what the average income is for tax purposes. A simple random sample of 1000 household reveals the following information. The average household income for the sample is $21,000. The median income of the sample is $13,000. The SD of the sample is $10,000.

a. Based on the above information, what is the estimate of the average household income in this county?

b. Find a 92% confidence interval for the average household income in this county.

(10 pts.)

Problem 2. One hundred draws were made from a box with unknown contents. A 95% confidence interval for the average of the tickets in the box was then computed. It is true that,

a. the SD of the box was estimated with the SD of the population.

b. a 68% confidence interval computed from the same data will be shorter ( from endpoint to endpoint) then the 95% confidence interval.

c. if the number of draws is quadrupled, and a new 95% confidence interval is computed, we expect the length of the new interval to be about one-quarter that of the original 95% confidence interval.

d. both a and b are true.

e. all of the above statements are true.