# Midpoint Theorem

Geometry Level 5

In trapezium $$ABCD$$, $$AB||CD$$ and $$AB=2CD$$. $$M,N$$ are the midpoints of $$AC$$ and $$BD$$ respectively. Let the perimeter of $$ABCD$$ be $$a$$ and the perimeter of quadrilateral $$CDMN$$ be $$b$$. Find $$a\div b$$.