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