how many people score 800 on the math section of the SAT.?

Well...if you assume this is a normal (Gaussian) distribution: an 800 is:

(800-518)/115 = 2.45 standard deviations above the mean

If someone looks at a normal distribution table:

http://www.statsoft.com/textbook/sttable.html

The probability of being 2.45 standard deviations or above is:

0.5 - 0.4929 = 0.0071

Roughly 0.7%.

For the true answer...I think its lower than 0.7%

*laugh*

I personally know the fifth-grader who got 800.