[Math] Probability of drawing balls without replacement in first and last draw

probability

If there are two red, three blue and four green balls in a bag and if three balls are drawn successively without replacement then probability of getting first draw as blue ball and third draw as red ball is what?

I did $P(\text{BRR})+P(\text{BBR})+P(\text{BGR})=\frac{42}{504}$

Best Answer

The probability that the first draw is blue is $1/3$.

Drawing from what's left, the probability that the next two balls are red is $(2/8)(1/7) = 1/28$.

Drawing from what's left, the probability that the second ball is not red, but the third ball is, is $(6/8)(2/7) = 3/14$.

So the overall probability is

$$P = \frac{1}{3}\frac{1}{4} = \frac{1}{12}.$$