Question

A box contains five sets of balls while there are 3 balls in each set. Each set of balls has one color which is different from every other set, what is the least number of balls that must be removed from the box in order to claim with certainty that a pair of balls of the same colour has been removed? 

 (a) 6 (b) 7 (c) 8 (d) 9

Answer 1

Now, any further removal of balls from any set will ensure that removed ball is of the same colour as one of the already removed balls, thus constituting a pair of the removed balls of the same colour.

Hence, minimum no. of removed balls = 6