AchyuthReddy wrote:

How many parallelograms are formed when a set of five parallel lines intersect another set of four parallel lines ?

A) 120

B) 60

C) 36

D) 20

E) 10

To form a parallelogram two parallel lines must intersect with two parallel lines

First case we have to select 2 parallel lines from 5 i.e. = 5C2

Second case we have to select 2 parallel lines from 4 i.e. = 4C2

Therefore total no. parallelogram formed = 5C2 * 4C2 = 10 * 6 = 60

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