Normal distribution of a final exam

steller

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A statistics teacher believes that the final exam grades for her elementary statistics class have a normal distribution with a mean of 82 and a standard deviation of 8

Find the score which separates the lowest 20% of the scores from the highest 80% of the scores.

I used the calculator.

\(\displaystyle invorm(.2) = -.8416 \)

\(\displaystyle 8( -.8416) + 82 = 75.26 \)

Now, the books examples(not this problem) strip the negative away after the invorm command.
So if \(\displaystyle invorm(.2) = -.8416 \) a negatve number do i use the negative or strip it away?
 
A statistics teacher believes that the final exam grades for her elementary statistics class have a normal distribution with a mean of 82 and a standard deviation of 8

Find the score which separates the lowest 20% of the scores from the highest 80% of the scores.

I used the calculator.

\(\displaystyle invorm(.2) = -.8416 \)

\(\displaystyle 8( -.8416) + 82 = 75.26 \)

Now, the books examples(not this problem) strip the negative away after the invorm command.
So if \(\displaystyle invorm(.2) = -.8416 \) a negatve number do i use the negative or strip it away?
If you don't know what the calculator is trying to tell you with the minus sign, figure it out by what the sign has to be to give you a sensible result. Isn't it likely the score for the bottom 20% will be LESS than the mean score?
 
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