# 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?

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 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(57219)   (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? ----- Find the z-score with a left tail of 0.81. invNorm(0.81) = 0.8779 --- Use x = zs + u to find "s" 12.10 = 0.8779*s + 11 --- 0.8779s = 1.1 sigma = 1.2530 ================ Cheers, Stan H.