A Problem of Gifts

It was Diwali day. A day to exchange gifts. Two fathers gave their sons some money. One father gave his son Rs. 150/- and the other Rs. 100/ But when the two sons counted their money, they found that between them they had become richer by only Rs. 150/.
How do you explain this ?

One of the fathers is the son of the other father. The problem posed would seem as if there are altogether four persons concerned. But that is not so. The three persons are grandfather, father and son. The grandfather gave his son Rs. 150/- and the latter passed on Rs. 100/- of them to the grandson (i.e. his son). Thus increasing his own money by Rs. 50/-.