I found the answers to this question on this website (

TUTORIAL SHEET 1 ? MA4704)

They are very different from my answers (it's an even problem, I can't check the back of the book). Can anyone walk me through one of a or b, and one of c or d?

Assume that X is normally distributed with a mean of 6 and a standard deviation of 3. Determine the value for x that solves each of the following.

a) P(X>x) = 0.5

My answer: x=6

Mr F says: Correct.
Other site's answer: x=7.5

Mr F says: Wrong.
b) P(X>x) = 0.95

My answer: x=10.95

Mr F says: Correct.
Other site's answer: x=8.85

Mr F says: Wrong.
c) P(x<X<9) = 0.2

My answer: x=7.095

Mr F says: Correct.
Other site's answer: x=7.08

Mr F says: Correct. The issue here is one of accuracy. A more correct answer is somewhere between these two answers.
d) P(3<X<x) = 0.8

My answer: x=11.235

Mr F says: Correct.
Other site's answer: x=7.9

Mr F says: Wrong.