SOLUTION: A major cell phone service provider has determined that the number of minutes that its customers use their phone per month is normally distributed with a mean equal to 445.5 minute

Question 663575: A major cell phone service provider has determined that the number of minutes that its customers use their phone per month is normally distributed with a mean equal to 445.5 minutes with a standard deviation equal to 177.8 minutes. The company is thinking of charging a lower rate for customers who use the phone less than a specified amount. If it wishes to give the rate reduction to no more than 12 percent of its customers, what should the cut off be?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A major cell phone service provider has determined that the number of minutes that its customers use their phone per month is normally distributed with a mean equal to 445.5 minutes with a standard deviation equal to 177.8 minutes. The company is thinking of charging a lower rate for customers who use the phone less than a specified amount. If it wishes to give the rate reduction to no more than 12 percent of its customers, what should the cut off be?
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Find the z-value with with a left-tail of 12%.
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invNorm(0.12) = -1.1750
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Find the x-value that corresponds:
x = z*s + u
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x = -1.1750*177.8+445.5 = 236.59
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Cheers,
Stan H.
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