normal distibution standard deviation

[mittman84]

I feel really dumb asking this question, but it is in my assignment that is due tomorrow and i am drawing a blank, and i have to figure out all this stuff by myself since my teacher is worthless. In in a certain normal distibution of X, the probability is .5 that X is less than 500, and the probability is .0227 that X is greater than 650, what is the standard deviation of X?