Hi,
My Question is the following:

11 parallel lines are intersected by another 9 parallel lines.Then how many parallelograms are formed?

Name : Moorthy
Level : Secondary
And I am a software engineer.

With warm Regards
Moorthy

There is a simple way to count:

A unique parallelogram will be formed by any two lines from the first set, and any two lines from the second set.

So count the ways of choosing 2 lines from 11 (order does not matter) AND choosing 2 lines from 9 (order does not matter).

Since this is an AND (we must do both) you multiply those two numbers to get the numbers of parallelograms

Walter Whiteley