AP EAPCET 23-Aug-2021 Shift 2 Paper

Given, 10 parallel lines and m parallel lines since one parallelogram can be formed by the intersection on one pair of parallel lines with another pair of another set of parallel lines.
∴ Number of parallelograms =‌10C2.‌mC2
⇒675=

10×9

2

×

m(m−1)

2

⇒30=m(m−1) ⇒m2−m−30=0
⇒(m−6)(m+5)=0 ⇒m=6