Question

A set of 4 parallel lines intersect with another set of 5 parallel lines. How many
parallelograms are formed?
(A) 20 (B) 48 (C) 60 (D) 72

Answer 1

This question can be understood as if m parallel lines intersect another n parallel lines, selecting a combination of 2 lines out of m lines and 2 lines out of n lines results in a selecting a parallelogram.

So number of parallelograms possible is mC2 * nC2 = 5C2*4C2 = 10*6 = 60 (option C)