In a bag of marbles you have three green, two yellow, six blue, and nine red marbles. what is the probability of picking a yellow marble from the bag?

The answer is 1/10.

There are in total 20 marbles in the bag:
3 green + 2 yellow + 6 blue + 9 red = 20 marbles

There are 2 yellow marbles of total 20 marbles. 2 of 20 can be expressed as:
2/20 = 1/10.

Therefore, the probability of picking a yellow marble from the bag is 1/10.

When you have multiplying with same base, you add the power, for example here : z^6 * z^3 = z^(6+3) = z^9.

When you have dividing with the same base, you substract it, for example here : z^9/z^4 = z^(9-4) = z^5.