A bag contains 6 green balls and 7 white balls. If two balls are drawn simultaneously, what is the probability that both balls are the same colour?  Answers
A) 2 / 7	B) 3 / 10	C) 5 / 11	D) 6 / 13	E) 11 / 21

Rationale: "the total number of ways to draw two balls is 13 c 2 = 78 the number of ways to draw two green balls is 6 c 2 = 15 the number of ways to draw two white balls is 7 c 2 = 21 p ( two balls of the same colour ) = 36 / 78 = 6 / 13 the answer is d ."
Answer: D