CEMC Fermat, 2011

Combinatorics Difficulty 3.0 AMC 10/12 Find the answer Canada

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?

(A) $6$ (B) $9$ (C) $4$ (D) $7$ (E) $8$

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