SOLUTION: A normal random variable X has a mean of 11. The probability that X is less than 12.10 is 0.81. What is the standard deviation of X?

Question 407226: A normal random variable X has a mean of 11. The probability that X is less than 12.10 is 0.81. What is the standard deviation of X?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A normal random variable X has a mean of 11. The probability that X is less than 12.10 is 0.81. What is the standard deviation of X?
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Find the z-score with a left tail of 0.81.
invNorm(0.81) = 0.8779
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Use x = zs + u to find "s"
12.10 = 0.8779*s + 11
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0.8779s = 1.1
sigma = 1.2530
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Cheers,
Stan H.
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