Question

This exercise uses the normal probability density function and requires the use of either technology or a table of values of the standard normal distribution.

The cash operating expenses of the regional phone companies during the first half of 1994 were distributed about a mean of $29.96 per access line per month, with a standard deviation of $2.85. Company A's operating expenses were $29.00 per access line per month. Assuming a normal distribution of operating expenses, estimate the percentage of regional phone companies whose operating expenses were closer to the mean than the operating expenses of Company A were to the mean. (Round your answer to two decimal places.)

Answer 1

Let X: Operating expenses of regional phone companies

To find

P(29<X<30.92)

As the mean for company A is 29 that is it is $0.96 away from the original mean so all those companies are considered whose mean lies in +/- 0.96 of 29.96.

so converting to standard normal

  

Hence the answer is 0.2662.