A gumball machine that randomly dispenses one gumball at a time contains 13 red, 5 blue, 1 white, and 9 green gumballs. What is the least number of gumballs that Wally must buy to guarantee that he receives 3 gumballs of the same colour?
If you have 7 gumballs, they might consist of 2 red, 2 blue, 1 white, and 2 green.
The eighth gumball must be the third of a color.
