Olympiad workbookIOQMPermutation and Combination
Let P be a convex polygon with 50 vertices. A set F of diagonals of P is said to be minimally friendly if any diagonal d F intersects at most one other diagonal in F at a point interior to P . Find the largest possible number of elements in a minimally friendly set. F .
Correct answer
71
Step-by-step solution
Total number of non-intersecting diagonals A₁ A₃, A₁ A₄, A₁ A₅, , A₁ A₄, 47 Total number of intersecting diagonals at only one point to the non-intersecting diagonals A₂ A₄, A₄ A₆, A₆ A₈, , A₄₈ A₅₀ 24 Total =47+24=71