Math
posted by Lori .
The total amount being spent on personal calls in a month by employees of a company follows a normal distribution with a mean of $900 and a standard deviation of $50. Find the probability that in a randomly selected month the amount spent on personal calls is less than $750

The standard deviation, σ, is $50. The mean is $900.
To spend less than $750 means that the spending is less than mean  3σ.
The probability of this happening, assuming the spending follows the normal distribution curve, can be found from the normal distribution tables, for example:
http://www.math.unb.ca/~knight/utility/NormTble.htm
where the probability for the tail end of 3σ is 0.001350, or 0.135%.