We have a square grid. In how many ways we get to the point [20,30], if we can not get points [5,5], [15,10] [15,10] [17,23]? The starting point is [0,0], we can only move up and to the right. Thanks
My solutions:
$$ \binom{50}{20} - \binom{10}{5}\binom{40}{15} - \binom{25}{10}\binom{25}{10}...