Question

If m parallel lines in plane are intersected by n parallel lines, then number of parallelograms formed is

• A. $\frac{m!n!}{{(2!)}^2}$
• B. $\frac{m!n!}{(m-2)!(n-2)!}$
• C. $\frac{m!n!}{{(2!)}^2(m-2)!(n-2)!}$
• D. $\frac{(m+n)!}{(m+n-2)!2!}$

Answer 1

The correct option is C $\frac{m!n!}{{(2!)}^2(m-2)!(n-2)!}$

${}^m{C}_2.{}^n{C}_2$