Assume that we have a box containing 7 blue balls and 9 red balls. Assume that we pick (and remove) 2 balls. Then we pick one extra ball later. What is the probability that the third ball is blue knowing that the previous two balls were both red?

Question

Assume that we have a box containing 7 blue balls and 9 red balls. Assume that we pick (and remove) 2 balls.  Then we pick one extra ball later. What is the probability that the third ball is blue knowing that the previous two balls were both red?

perl · Answer

you now have a total of how many balls after picking 2 red balls ?

miracrown · Answer

The first two balls we removed are red. So, that leaves 7 blue balls, and 7 red balls
So, the probability the third ball is blue, is 7/14 = 1/2

anonymous · Answer

thank you