A box contains 4 black, 3 red and 6 green marbles. 2 marbles are drawn from the box at random. What is the probability that both the marbles are of the same color?  Choose the correct choice from the following:
A) 24 / 78	B) 24 / 709	C) 24 / 76	D) 24 / 71	E) 24 / 72

Rationale: explanation : total marbles in a box = 4 black + 3 red + 6 green marbles = 13 marbles 2 marbles are drawn from 13 marbles at random . therefore , n ( s ) = 13 c 2 = 78 ways let a be the event that 2 marbles drawn at random are of the same color . number of cases favorable to the event a is n ( a ) = 4 c 2 + 3 c 2 + 6 c 2 = 6 + 3 + 15 = 24 therefore , by definition of probability of event a , p ( a ) = n ( a ) / n ( s ) = 24 / 78 answer : a
Answer: A