Play with Polygons

For 100 - sided polygon

1. Find the number of 20 sided polygon that can be formed in it by joining its vertices(With no side common with that of 100 - sided polygon).

   your answer can be represented as $a \times \overset { b }{ \underset { c }{ C } }$ : C is combinatorics symbol

2. Find the number of rectangles that can be formed by joining its vertices(Considering it to be regular(only for this case)). Let it be $d$ .

3. Find the number of point of intersections of the diagonals in the interior of polygon such that none intersections coincide . Let it be $e$ .

Enter your answer as $min$ { $a + b + c + d + e$ }

Try my set : Let's play with polygons