Question

A new phone system was installed last year to help reduce the expense of personal calls that were being made by employees. Before the new system was installed, the amount being spenton personal calls followed a normal distribution with an average of $600 per month and a standard deviation of $50 per month. Refer to such expenses as PCE's (personal cell expenses). Using the distribution above, what is the probability that a randomly selected month had a PCE of between $475.00 and $690.00?

Answer 1

Given that

A normal distribution with an average of $600 per month,

A standard deviation of $50 per month,

The probability that a randomly selected month had a PCE of between $475.00 and $690.00 is

we all know that,

So,

we can also write this as

From the standard normal distribution table, we can get P values from Z

P(475 < X<690) = 0.9281393 ~ 0.92814