Posted by **Lori** on Saturday, April 17, 2010 at 11:18pm.

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

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**MathMate**, Sunday, April 18, 2010 at 7:48am
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%.

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