A major cell phone service provider has determined that the number of minutes th
ID: 3131726 • Letter: A
Question
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 changing its fee structure so that anyone who uses the phone less than 250 minutes during a given month will pay a reduced monthly fee. Based on the available information, what percentage of current customers would be eligible for the reduced fee?
About 36.4%
Approximately 52%
About 86.6%
About 13.6%
About 36.4%
Approximately 52%
About 86.6%
About 13.6%
Explanation / Answer
We first get the z score for the critical value. As z = (x - u) / s, then as
x = critical value = 250
u = mean = 445.5
s = standard deviation = 177.8
Thus,
z = (x - u) / s = -1.099550056
Thus, using a table/technology, the left tailed area of this is
P(z < -1.099550056 ) = 0.135764106 = 13.6% [ANSWER]
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