Question

A set of 4 parallel lines intersect with another set of 5 parallel lines. how many parallelograms are formed?

Answer 1

This is a question for Permutations and Combinations. For a parallelogram, you need 2 pairs of parallel lines. So we can "choose" any two lines from the first set of 4 parallel lines 'and' choose any two lines from the second set of 5 parallel lines.

Hence the value we need is

4C2 × 5C2 = 6 × 10 = 60

Thus 60 parallelograms are formed.