A bag contains 5 green balls and 8 white balls. If two balls are drawn simultaneously, what is the probability that both balls are the same colour?
Options:
A) 3 / 7
B) 6 / 11
C) 12 / 21
D) 19 / 39
E) 29 / 49

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 5 c 2 = 10 the number of ways to draw two white balls is 8 c 2 = 28 p ( two balls of the same colour ) = 38 / 78 = 19 / 39 the answer is d ."
Answer: D