A survey is being planned to determine the mean amount of time corporation executives watch television. A pilot survey indicated that the mean time per week is 17 hours, with a standard deviation of 4.5 hours. It is desired to estimate the mean viewing time within one-quarter hour. The 90 percent level of confidence is to be used.

How many executives should be surveyed?

Question

A survey is being planned to determine the mean amount of time corporation executives watch television. A pilot survey indicated that the mean time per week is 17 hours, with a standard deviation of 4.5 hours. It is desired to estimate the mean viewing time within one-quarter hour. The 90 percent level of confidence is to be used.
  
How many executives should be surveyed?

anonymous · Answer

First you need to find the z-value for a 90% confidence interval.  Then use the equation:

n = [z ( standard deviation / mean)] ^2

anonymous · Answer

n= [ z ( 4.5/17)] ^2

anonymous · Answer

Thank you that is what I have been trying to do the Z value is either 1.64 or 1.65 but I cant come up with the answer XC