Level 5 Math
posted by Linda
A bag contains 300 marbles, each of the same size, but in six different colours. Suppose there are 50 marbles of each colour. What is the smallest number of marbles I must pick to be absolutely sure that there are 4 marbles of the same colour among the marbles I have picked blindfolded?
suppose you pick 18 marbles -- 3 of each color. The 19th marble must be the same color as one of the 18.