(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An urn contains one white chip and a second chip that is equally likely to be white or black. A chip is drawn at random and returned to the urn. Then a second chip is drawn. What is the probability that a white appears on the second draw given that a white appeared on the first draw.

2. Relevant equations

3. The attempt at a solution

I am trying to use the equation

P(white2 | white 1) = p(white2 and white 1) / P(white1)

The back of the book says the answer is 5/6.

I am fairly sure that P(white1) is (1/2)(2/2) + (1/2)(1/2) or .75

So that would make p(white2 and white1) to be 5/8 which I can't for the life of me see why.

Any ideas on how to do this? The examples we work out in class are so elementary and I get bored. The problems assigned for homework as very hard (or at least this seems much much harder).

Thanks for any help!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Urn Probability Question

**Physics Forums | Science Articles, Homework Help, Discussion**