You have six balls - three red and three black. All the red balls weigh differently, i.e. one of them is heavy, the other medium, and the third light. Each red ball has a black twin of the same weight. A heavy and a light ball put together weigh as much as two medium balls.

What is the least number of weighings required on a balancing scale to determine which is which?

(In reply to

re: A different solution by atul)

Not sure what you mean. For example, if you have

1 red heavy and 1 red light and weigh it against 1 black heavy and 1 black light then the scale will balance.

Then, if you pick up the 1 red heavy and 1 black heavy then it will balance the next try. However, you don't know which ball is which because the scale always balances.