There are 12 yellow, 21 blue, and 17 red marbles in a bag. You take three marbles out of the bag, one at a time, without replacement. What is the probability that the first marble is yellow and the next two marbles are red?

First you have to know the total amount of marbles in the bag (50)
Next you have to determine whether it’s am adding question or a multiplying question. In this case, you are multiplying because you are doing a and b. (You would add if it said a or b).
Third break it down.
12 yellow marbles out of 50
So the chance to get a yellow marble
is 12/50 or 6/25

There is no replacement meaning that there are now only 49 marbles left.
17 red marbles out of 49
The probability of getting a red
marble is 17/49

There is no replacement again meaning that there are now 48 marbles.
This time, you also have to subtract one red marble away since once was taken in the second drawing.
16 red marbles out of 48
Probability is 16/48 or 1/3

Now multiply all of the probabilities together to find the final answer.

(6/25)*(17/49)*(1/3)= 0.02775
2.78%