A bag has 3 red marbles and 5 blue marbles. If you randomly pull out 4 marbles, what is the probability of getting two red ones and two blue ones?
There are 1680 possible combinations for pulling out marbles. (8*7*6*5)
There are 6 possible combinations for getting 2 red and 2 blue. (RRBB, RBRB, BRBR, BBRR, BRRB, and RBBR)
\(6\over1680\)\(\Rightarrow\)\(1\over280\)
The answer is \(1\over280\)