Question 314031: I am working my statistics class, and am having issues finding the correct formula for finding the value x such that P(X > x) is equal to a number, given that, X is a normal random variable with the mean equaling to a number and standard deviation equaling to a number.
I have been using the following formula, but it is not working right:
z = X - mean / standard deviation
I did not want you to work the problem for me, I just need assistance without getting the answer.
Thank You in advance...Rosanna
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! I am working my statistics class, and am having issues finding the correct formula for finding the value x such that P(X > x) is equal to a number
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Let's say P(X>x) = k
That means you have a right tail of "k" on the z-distribution curve.
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Use invNorm(1-k) to find the z-value that has that right tail.
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Then use x = zs+u to find the value of x you are asked to find.
Cheers,
Stan H.
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