##### Monthly utility bills are normally distributed with a mean of \$120

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and a standard deviation of \$16?
a) what is the probability that a randomly selected bill will be less than \$80 per month?

b) what is the probability that a bill will be greater than \$140 per month?

c) what is the probability that a bill will be between \$100 & \$140 per month?

if someone could explain this to me, this chapter has me lost
Apr 22nd, 2015

a)  Z = 80-120 / 16 = -2.5 standard deviations from the mean

look up on Z chart to find probability:  P = .0062 or 0.062%

b) Z = 140-120 / 16 = 1.25 standard deviations from the mean

on Z chart, the probability = 0.8944, but that is the probability for LESS THAN \$140

for GREATER THAN we need to subtract it from 1:  1 -0.8944 = 0.1056 or 10.56%

c) for between \$100 and \$140 we have to subtract the probability of each

P(Z at \$140) = 0.8944

P(Z at \$100) = 0.1056

The difference is 0.7888 or 78.88%

Apr 22nd, 2015

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Apr 22nd, 2015
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Apr 22nd, 2015
Dec 9th, 2016
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