ASSIGNMENT
1. The 90% confidence interval for the mean one-way commuting time in New York City is
5.22 < u < 5.98 minutes. Construct a 95% confidence interval based on the same data.
Which interval provides more information?
2. If the variance of a national accounting examination is 900, how large a sample is needed to estimate the true mean score within 5 points with 95% confidence?
3. Thirteen randomly selected people were asked how long they slept at night. The mean time was 7.1 hours, and the standard deviation was 0.78 hour. Find the 99% confidence interval of the mean time. Assume the variable is normally distributed.
4. Find the 90% confidence interval for the variance and standard deviation for the lifetime of disposable camera batteries if a sample of 19 disposable camera batteries has a standard deviation of 2.1 months. Assume the variable is normally distributed. Do you feel that the lifetimes of the batteries are relatively consistent?
5. A researcher wishes to estimate, with 95% confidence, the proportion of people who own a home computer. A previous study shows that 40% of those interviewed had a computer at home. The researcher wishes to be accurate within 2% of the true proportion. Find the minimum sample size necessary.