Given that on one section of the sat the mean is 500 and the standard deviation is 100, what is the approximate probability of a student scoring 400 or lower or 500 or higher on the test?

We are to find for the probability when X≤400 or X≥500

We use the z score formula: z = (x - u) / s

when X≤400, the z is:

z = (400 - 500) / 100 = - 1

when X≥500, the z is:

z = (500 - 500) / 100 = 0

SO from the standard probability tables, the probability at:

P (z ≤ - 1 or z ≥ 0) = 0.6587