According to an IRS study, it takes a mean of 330 minutes for taxpayers to prepare, copy and electronically file a 1040 tax form. The distribution of times follows the mormal distribution and the standard deviation is 80 minutes. A consumer watchdog agency selects a random sample of 40 taxpayers.
a. What is the standard error of the mean in this example ?
b. What is the likelihood the sample mean is greater than 320 minutes ?
c. What is the liklihood the sample mean is between 320 and 350 minutes ?
d. What is the likelihood the sample mean is greater than 350 minutes ?