Scores on a common final exam are normally distributed with mean 71 and standard deviation 9. Department policy is that the top 10% of students receive an A. The minimum exam score to be awarded an A is about:
a)95 b)83 c)98 d)87 e)90

Question

Scores on a common final exam are normally distributed with mean 71 and standard deviation 9. Department policy is that the top 10% of students receive an A.  The minimum exam score to be awarded an A is about:
a)95 b)83 c)98 d)87 e)90

anonymous · Answer

For some reason I keep getting 59.4

kirbykirby · Answer

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kirbykirby · Answer

So if the minimum score is $c$, and $X$ is the random variable for people's scores, then you can say that $P(X < c)=0.9$ [or equivalently, $P(X > c)=0.10$ ]

anonymous · Answer

So the answer would be 90.. But how am i getting 59 =/

kirbykirby · Answer

Just to be certain, do you understand why I say that $P(X < c)=0.9$?

anonymous · Answer

I have no idea, I'm so lost lol

kirbykirby · Answer

Hm. do you understand the picture I drew?

anonymous · Answer

I tried putting the problem in my calculator and thats how i got 59.4

kirbykirby · Answer

WHat did you try putting into your calculator?

anonymous · Answer

I understand the mean being in the middle, but i don't understand the shaded region. And I entered the problem using invNorm

kirbykirby · Answer

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