Before a new phone system was installed, the amount a company spent on personal calls followed a normal distribution with an average of $900 per month and a standard deviation of $50 per month. Refer to such expenses as PCE's (personal call expenses). Using the distribution above, what is the probability that during a randomly selected month PCE's were between $775.00 and $990.00?
A) .0001
B) .9999
C) .9579
D) .0421

Question

Quizplus · Accepted Answer

The probability that PCE's are between $775 and $990 can be found by calculating the z-scores for these values and using the standard normal distribution table. The z-score for $775 is (775-900)/50 = -2.5, and for $990 is (990-900)/50 = 1.8. The probability of z being between -2.5 and 1.8 is approximately 0.9579.

Before a New Phone System Was Installed, the Amount a Company