Marvin the fly starts at $(0,0).$ Each step, Marvin moves one unit right or one unit up. He is trying to get to the point $(5,7)$. However, at $(4,3)$ there is a frog that will eat him if he goes through that point. In how many ways can Marvin reach $(5,7)$?
(All other answers to this question were wrong)
First, lets find how many ways to get to (4, 3) then from (4, 3) to (5, 7) then subtract that from the ways to go from (0, 0) to (5, 7).
The formula for going from one point two another on a perfect grid is ((x0, y0) is the first point and (x1, y1) is the second point) (abs(x1 - x0) + abs(x1 - x0)) choose abs(x1 - x0) or abs(y1 - y0)
This should be enough to get you started on how to solve this problem.
(Btw, i got it right on aops and the answer is 617) (yes i know this is aops.)