Q1. In a recent study of 250 female freshmen showed that 70 did not want to work after marriage. Find the 95% confidence interval of the true proportion.
Q2. Find the 99% confidence interval for the variance and standard deviation for the lifetime of batteries if a sample of 40 has a standard deviation of 3.4 months. Assume the variable is normally distributed.
Q3. A researcher wishes to test the claim that the average age of lifeguards is greater than 22 years. The researcher sampled 56 lifeguards and found an average of 23.7 years with a standard deviation of 2 years. Test the claim at "alpha" = 0.05.
Q4. Ten randomly selected cars were stopped and the tread depth of the left front tire measured. The mean was 0.12 inch, and the standard deviation was 0.02 inch. Find the 90% confidence interval of the mean depth.