The diagram shows the contents of a jar of marbles. You select two marbles at random. One marble is drawn and not replaced. Then a second marble is drawn. What is the probability of selecting a red marble and then another red marble?

three over sixty-four
one-fourth
one over twenty
one over thirty

Question

The diagram shows the contents of a jar of marbles. You select two marbles at random. One marble is drawn and not replaced. Then a second marble is drawn. What is the probability of selecting a red marble and then another red marble?

    three over sixty-four
    one-fourth
    one over twenty
    one over thirty

nathan917 · Answer

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rajee_sam · Answer

The jar has R = 4; B = 7; G = 5

two marbles drawn at random without replacement.

P(red, red) = 4/16 * 3/13 = 3/52

anonymous · Answer

The probability of 2 red marbles is:

P(1st red) times P(2nd red)

Since you are not replacing the first marble, you have less marbles left on the second draw:

(4/16) times (3/15)  =  1/20

The 4/16 comes from "4 out of 16 are red"

The 3/15 comes from "3 out of 15 are red"  ->  One red marble was taken and 15 total remain before the second draw.

So,

1/20

anonymous · Answer

All good now, @nathan917 ?

nathan917 · Answer

Yes. Thanks!

anonymous · Answer

uw!  Good luck to you in all of your studies and thx for the recognition! @nathan917