4. A local electronics firm wants to determine their average daily sales (in dollars.) A sample ofthe sales for 36 days revealed average sales of $139,000. Assume that the standard deviationof the population is known to be $12,000.

a. Provide a 95% confidence interval estimate for the average daily sales.

b. Provide a 97% confidence interval estimate for the average daily sales.

5. The Highway Safety Department wants to study the driving habits of individuals. A sample of 81 cars traveling on the highway revealed an average speed of 67 miles per hour with a standard deviation of 9miles per hour.

a. Compute the standard error of the mean.

b. Determine a 99% confidence interval estimate for the speed of all cars.

6. In order to determine the summer unemployment rate among college students, a pilot sample was taken;and it was determined that ten percent of the individuals in the sample were unemployed. Using theresults of the pilot study and a 95% confidence, what size sample would be required to estimate theproportion of unemployed college students if we want the margin of error not to exceed 3 percent? 7. In order to estimate the proportion of individuals who read at least one book per month, a randomsample of individuals was selected and they were asked whether or not they read at least one book permonth. Their responses are shown below.

Responses	Frequency
Yes, I read at least one book per month	640
No, I do not read at least one book per month	160

Develop a 95% confidence interval for the proportion of people in the population who read at leastone book per month. 8. a survey conducted to determine among other things, the cost of holidays, 164 individuals were randomly sampled. Each was asked to assess the total cost of his or her most recent holiday. Theaverage cost was $1386. Assuming that the standard deviation was $400 estimate the populationmean cost of holidays with 99% confidence.