probability

"A hat contains 2 red marbles, 3 blue marbles, and 4 green marbles.  You choose two different marbles at random.  What is the probability that they are the same color?"

            red           blue          green  

$p=\frac{2}{9}\times \frac{1}{8}+\frac{3}{9}\times \frac{2}{8}+\frac{4}{9}\times \frac{3}{8}=\frac{5}{18}=0.278$