Question

Chapter 9
3. A sample of 25 items yields = 60 grams and s = 9 grams. Assuming a normal parent distribution, construct a 99 percent confidence interval for the population mean weight.

4. Of a random sample of 900 trucks at a bridge, 360 had bad signal lights. Construct a 99 percent confidence interval for the percentage of trucks that had bad signal lights.

5. Suppose that 80 percent of the voters in a particular region support a candidate. Find the probability that a sample of 1600 voters would yield a sample proportion in favor of the candidate within 1 percentage points of the actual proportion.

Answer 1

1)

t critical value at 0.01 level with 24 df = 2.797

99% confidence interval for is

- t * S / sqrt(n) < < + t * S / sqrt(n)

60 - 2.797 * 9 / sqrt(25) < < 60 + 2.797 * 9 / sqrt(25)

54.9654 < < 65.0346

99% Ci is ( 54.9654 , 65.0346 )