Question

One boy and girl going on bike.Suddenly a police stop them and asked what is relation between them.The boy told him that her father in law is the father of my father in law. what is relation between them

Answer 1

The girl is the boy's mother in law. 

Answer 2

The girl is the boy's mother in law.

As,

Let's think the boy is =x

the girl is =Y

Girl's husband =YH

Girl's husband's father=YHF

Now,The boys father in laws father =YH's father.

So the boy is the son in law of the girl.

Hope it helps.