# Probability that the first blue marble is the third marble drawn.

A bag contains five white and three blue marbles. Successive marbles are drawn at random from the bag. What is the probability that the first blue marble is the third marble drawn.

Answer in back of book: 5/28

My thinking:

P(First ball not being the first blue marble) = 7/8

P(Second ball not being the first blue marble) = 6/7

P(Third ball being the first blue marble) = 1/6

P(final) = 7/8 * 6/7 * 1/6 = 1/8

Where am I going wrong?

• The probability that the first ball is not the first blue one is $\frac 58$. – lulu Jan 4 '16 at 13:20
• Ah , I understand now. Actually I misunderstood the question. I thought each of the blue marbles were sort of assigned a first, second and third. So for the first selection one could select any white marble or the second or third blue marble but not the first blue marble. Thanks – Kantura Jan 4 '16 at 13:25