Originally Posted by

**daivinhtran** 10 black, 20 white, 40 red

The question is what is probability when we reach 5 of them, and we have 2 white, 2 red, 1 black.......

And some guy solved this question on youtube, and his answer was 12.2%

He solve like : (20C2 x 40C2 x 10C1)/ (70C5)

I know he was right. BUt I don't understand it

I solve by another way like :

Doing it your way, you would calculate the probability for each of the 30 possible ways to draw 2W, 2R and one B. So, to draw WWRRB in that order, you get

(20/70)(19/69)(40/68)(39/67)(10/66)

Each iteration of 2W, 2R, and 1B has an identical probability. So, multiply by 30, and you get 12.2%.

Can somebody explain me about first way?

I really can't make sense!!