A study was conducted to determine the mean number of weekly hours that adults in the US use computers at home. A random sample of 81 adults gives a mean weekly computer usage time of 8.5 hours. Based on prior studies, the population standard deviation is assumed to be 3.6 hours.
Which will provide the narrowest confidence interval? And Why?
a) using 2 samples of 200 each
b) using a sample size of 400
c) using a different sample of size 81
d) using a sample of size 36