Confidence interval for the true proportion

Reference no: EM1319229

Confidence interval for the true proportion.

1. A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine. The desired length of the insulation is 12 feet. It is known that the standard deviation in the cutting length is 0.15 feet. A sample of 70 cut sheets yields a mean length of 12.14 feet. This sample will be used to obtain a 99 percent confidence interval for the mean length cut by machine.

a. The critical value to use in obtaining the confidence interval is _______________

b. The confidence interval goes from ________ to ________.

c. Suppose the engineer had decided to estimate the mean length to within 0.03 with 99 percent confidence. Then the sample size would be ________.

2. The president of a university is concerned that the percentage of students who have cheated on an exam is higher than the 1 percent acceptable level. A confidential random sample of 1000 students from a population of 7000 revealed that 6 of them said that they had cheated on an exam during the last semester.

a. What is the critical value for the 90 percent one-sided confidence interval for the proportion of students who had cheated on an exam during the last 12 months?

b. What is the upper bound of the 90 percent one-sided confidence interval for proportion of students who had cheated on an exam during the last 12 months?

Reference no: EM1319229

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