Agreat way to visualize conditional probabilities is to think about a bag of marbles. in our initial bag of marbles we have 2 blue marbles, and 3 red marbles. therefore, we have a 2/5 chance of selecting a blue marble, and a 3/5 chance of selecting a red marble. selecting marbles when selecting a second marble, the probabilities have changed. we now have conditional probabilities for all of the different possible scenarios. marble image tree 2 based on the image above, what is p(b|a), the probability of pulling out a red marble, after having already pulled out a blue marble? p(a) is the probability of selecting a blue marble and p(a and b) is the probability of selecting a blue marble and a red marble. p(a and b) is different than p(b|a), the conditional probability of selecting a red marble, when a blue marble has already been selected. report as a decimal rounded to 2 decimal places, not a percent.