Find the number of integral points (integral points means that both the coordinates should be integer) exactly in the interior of the triangle with vertices (0,0),(0,1) and (21,0)

Number of integral points will be integral multiple of x- coordinates only as Y coordinates will be zero only within the triangle.

So number of integral points will be 20 like (1,0), (2,0), (3,0)... (20,0) excluding (0,0) and (21,0)