Six balls, numbered 2, 3, 4, 5, 6, 7, are placed in a hat. Each ball is equally likely to be chosen. If one ball is chosen, what is the probability that the number on the selected ball is a prime number?
(A) $\frac{1}{6}$
(B) $\frac{1}{3}$
(C) $\frac{1}{2}$
(D) $\frac{2}{3}$
(E) $\frac{5}{6}$
Of the numbers $2,3,4,5,6,7$, only the numbers $2,3,5$, and 7 are prime.

Since 4 out of the 6 numbers are prime, then the probability of choosing a ball with a prime number is $\frac{4}{6}=\frac{2}{3}$.

ANSWER: (D)