Normal Distribution - Find Area

Question

At a customer service call center for a large company, the number of calls received per hour is normally distributed with a mean of 170 calls and a standard deviation of 15 calls. What is the probability that during a given hour of the day there will be less than 144 calls, to the nearest thousandth?

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Answer 1

Pr ( x < 144 ) = Pr [ z = ( 144 - 170 ) / 15 = - 1.733 ] = from normal table .0415

Answer 2

First of all, 144 is almost 2 standard deviations out so that the answer will be close to 5%.

Actually z=-1.73 and the answer is .5-.4582=.0418.