Blue and Red Ball Problem

You have three bags and three labels. One bag has only red balls, one has only blue balls and one has both red and blue balls. Three labels are R, B and RB. R label was meant for the bag with only red balls, B label was meant for the bag with only blue balls and RB for the bag with both red and blue balls. Sam by mistake labelled the bags wrongly such that all the labels are wrong, how many minimum number of balls he should pick and from what bag , to correct the labels? It is given that each bag has unlimited number of balls to be picked.

Answer is 1 and it should be picked from the bag labelled as  RB.

What !! How ?? You were not expecting this .

 Lets find out how did this answer come out  

As it is given the label of all the bags are wrongly labelled , bag with label RB can either have all red balls or all blue balls.

Now sam will either get red ball or the blue ball.

Case 1: Sam gets a red ball
Bag with label RB is the bag with all the red balls.
Therefore, Bag with label B will contain all red balls .
We know 2 bags correctly so third bag with label R will contain both red and blue balls .

Case 2: Sam gets a blue ball.

Bag with label RB is the bag with all the blue balls

Therefore, Bag with label B will contain all red balls
we know 2 bags correctly so third bag with label R will contain both.

Reference Guru