Answer:
Letter A:
There is a 42.857143% chance of picking a black marble out of the bag. This is because there are 7 marbles total and 42.857143% of them(3/7) are black, so that is the probability.
Letter B:
There is a 14.285714% chance of picking this. The chance of picking a black black marble first is 3/7, which you multiply by the chance of picking a marble out on your second try without putting the first black marble back in ,which is 1/3. That gives you 1/7, or the percent above.
Letter C:
The probability of picking a black marble, replacing it, then picking another black marble is 18.367347%, or 9/49. You take the probability of picking out a black marble first, 3/7, and multiply it by the chance of picking another black marble after replacing the first one, which is also 3/7.
Letter D:
The probability is different for B and C because in B the chance for the second one is less because for the second pick there are less marbles and a third of them are black. In C the chance of picking a black marble in the second is the same as in the first because you are putting the original back in.
