There are 5 red balls 5 blue balls and 5 yellow balls in a b

There are 5 red balls, 5 blue balls and 5 yellow balls in a box. How many balls must be get out of the box to assure that there are at least 3 different color balls?

Solution

5 red balls, 5 blue balls and 5 yellow balls in a box

for lets assume the worst case.

we are taking one by one ball out of the box and all are coming with same colour.

So we can remove at most 4 balls to ensure that there is atleast one ball from each colour.

or, box should contain 11 balls atleast to have a at least all coloured ball