Rajiv said, pointing to a girl, “she is the only daughter of the father of my sister’s brother”. If so how is the girl related to Rajiv?

Solution :

From the information above we can conclude that the father has only one daughter who is the girl to find and the father has one son whom is Rajiv mentioned as sister's brother.

So, Rajiv has only one sister who is the only daughter of Rajiv's father.

So, Rajiv and the girl are brother and sister

So the correct option is 3). Sister