The lengths of long distance phone calls placed on a cell phone can be described by a Normal model with a mean of 7 minutes and a standard deviation of 2 minutes.If one call is randomly selected from wireless phone company records,what is the probability that it will have lasted more than 11 minutes?
A)0.0977
B)0.23
C)0.977
D)0.023
E)0.98

Question

Quizplus · Accepted Answer

We need to find P(X > 11), where X represents the length of a long distance phone call. We can standardize the variable by using z-score:
z = (11 - 7) / 2 = 2
Now we can look up the probability of z being greater than 2 in the standard Normal table, which gives us 0.0228. Therefore, P(X > 11) = 0.0228 or 0.023 when rounded to three decimal places. So, the correct choice is D.

The Lengths of Long Distance Phone Calls Placed on a Cell