Question 922148: The amount of snowfall falling in a certain mountain range is normally distributed with a mean of 74 inches, and a standard deviation of 12 inches. what is the probability that the mean annual snowfall during 36 randomly picked years will exceed 76.8 inches? (I know the answer I do not know how to get the answer)
Found 2 solutions by ewatrrr, stanbon:
Answer by ewatrrr(24785)   (Show Source):
You can put this solution on YOUR website! mean of 74 inches, and a standard deviation of 12 inches, n = 36
x= 76.8, z = 2.8//(12/sqrt(36)) = 1.4
P(xbar> 76.5) = P(z >1.4) = normalcdf(1.4, 100) = .0808 0r 8.08%
z-test was used as Population SD is known and sample size > 30
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A NEED to know is what sample size is thought to be sufficient
for using z-test WHEN Population SD is known...check with Your sources.
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Population SD unknown...t-test is generally called for.
 and tcdf function used.
Answer by stanbon(75887)  (Show Source):
You can put this solution on YOUR website! The amount of snowfall falling in a certain mountain range is normally distributed with a mean of 74 inches, and a standard deviation of 12 inches. what is the probability that the mean annual snowfall during 36 randomly picked years will exceed 76.8 inches? (I know the answer I do not know how to get the answer)
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t(76.8) = (76.8-74)/(12/sqrt(36)) = 2.8/(2) = 1.4
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P(x-bar > 76.8) = P(t > 1.4 when df = 35) = tcdf(1.4,100,35) = 0.3458
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Cheers,
Stan H.
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