Permutaion and Combination

Question

A bag contains 20 balls. 8 balls are green, 7 are white and 5 are red. What is the minimum number of balls that must be picked up from the bag blindfolded (without replacing any of it) to be assured of picking at least one ball of each colour?

Answer 1

16

 

8 greens in a row, then 7 whites in a row, then a red