A jar contains 3 black, 3 white and 1 green balls. If you pick two balls at the same time, what's the probability that one ball is black and one is white?	Choices.
A) 2 / 7
B) 5 / 7
C) 4 / 7
D) 3 / 7
E) 1 / 2

Rationale: p ( 1 st black , 2 nd white ) = 3 / 7 * 3 / 6 = 9 / 42 ; p ( 1 st white , 2 nd black ) = 3 / 7 * 3 / 6 = 9 / 42 . p = 9 / 42 + 9 / 42 = 18 / 42 = 3 / 7 . answer : d .
Answer: D