11 parallel lines are intersected by another 9 parallel lines.Then how many parallelograms are formed?
Name : Moorthy
With warm Regards
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