(Q). Consider a set of ‘m’ parallel lines and another set of ‘n’ parallel lines then what is the number of parallelograms thus formed by these parallel lines?
Solution:-
To get a parallelogram we need to select 2 lines from ‘m’ lines that can be done in ᵐC₂ ways, at the same time 2 lines from ‘n’ lines and that can be done in ⁿC₂ ways.
Hence total number of parallelogram is
= ᵐC₂×ⁿC₂ Answer
