Hey

I'm having major issues trying to figure this out...

In America, there are 2 primary standardized tests used by colleges to decide on admissions: SAT & ACT. In 2001, SAT scores had a mean of 500 & a standard deviation of 100, while ACT scores had a mean of 21.0 & a standard deviation of 4.7. In each case, the higher the mark the better the result & the greater the chance of being accepted for admission. Assume that the scores for students in general are Normally Distributed with means & standard deviations as stated above.

Question: Between what 2 scores do the central 80% of students score in the SAT tests?

Now this is what I have:

For the central 80% of SAT student test scores: pr(xL < X < xU) = 0.80

pr(xL < X < xU) = 0.80 = pr(X < xL) = 0.10 = xL =

pr(xL < X < xU) = 0.80 = pr(X < xU) = 0.90 = xU =

The central 80% of SAT test scores fall between

So I know thats the working formula, I just have no idea how to get the answer... I know we use our calculators to get the figures, but I cant remember how. Its driving me nuts, I've listened to my lectures about 6 times and gone over all my notes and this is making me draw a huge blank and I'm really confused.

Any help would be greatly appreciated!!