posted by jake on .
If there are 6 blue marbles and 2 red marbles in a bag, what is the probability of picking a blue marble then another blue marble if you do not replace the first marble P(B,B)? 3/4 x 5/7 or is it 3/4 x 6/7?
Prob = (6/8)(5/7) , which was your first choice
3/4 x 5/7, but that means you presume you took out a blue marble the first time. How do you know that you didn't take out a red marble, so you still have all six blue marbles when you pick the second time?
"... but that means you presume you took out a blue marble the first time"
yes, that is the case we wanted, and the 6/8 is the probability that would have happened, and one of the blue marbles has now been picked.
The Answer is The Probality of picking a pink Or Blue is 4 divide in 2 is 2 1.2