4. Lengths of Phone Calls, Part II

As in the previous exercise, suppose the lengths of phone calls to the receptionist of a small company are i.i.d. with a mean of 4 minutes and an SD of 10 minutes.

Let 1,2,...,X1,X2,...,Xn be the lengths of n calls in minutes, and let =1=1An=1ni=1nXi be the sample average length.

In each of the following parts, either find the chance exactly, or approximate it, or bound it. Do the best you can with the information given.

a) (|44|<10)P(|A44|<10)

b) (|25004|<0.4)