probability problem

Question

There is a bag with 3 yellow marbles 2 blue marbles and 1 green marble. The marbles are shooken up. I pull out 2 marbles one at a time. what is the probability I pick not green then blue. please answer quickly

Answer 1

There are 6 total marbles.

There is 1 green marble and 5 are NOT green marbles.

So probability first pick is not a green marble is 5/6.

We are left with 5 marbles, 1 of which is blue.

So probability second pick is a blue marble is 1/5.

Probability first pick is not a green marble and second pick is a blue marble is 5/6 * 1/5 = 5/30 = 1/6

Answer 2

Order matters here. The denominator is easy, P(3+2+1, 2) = P(6, 2) = 6 * 5 = 30

Not selecting a green first means selecting either a blue or yellow first. Then , we select a blue second.

We shall look at selecting a yellow and blue first separately.

We have 3 ways of selecting a yellow marble first, and then 2 ways of selecting a blue.

We also have 2 ways of selecting a blue marble first, then 1 way of selecting a blue.

(3 * 2 + 2 * 1) = 8

Then, the probability is 8/30 = 4/15