Question

The average score on a standardized test is 750 points with a standard deviation of 50 points. If 2,000 students take the test at a local school, how many students do you expect to score between 700 and 800 points?

Answer 1

I the average score is 750 and standard deviation ( sigma ) is 50 points, then score 700 - 800 is between (750 - 1 sigma) and (750 + 1 sigma).
That is 34.1 % + 34.1 % = 68.2 % of the whole population. 
2,000 · 0.682 = 1.364 
We expect 1,364 students to score between 700 and 800 points.