probability problem oh shi

You have two coins inside a bag, and you know that one of them is a double headed coin while the other is a normal heads/tails coin. You randomly pick one up from the bag and look at the coin; it's the heads side. You are not permitted to look at the other side of the coin (where's the fun in that?) and instead you have to find out what the chance is that the coin that you are looking at is the two headed coin. So, then, what is the probability?

In b4 half of /sci/ says 1/2

50%

It be 2/3
I'll leave the explanation to the next guy

in total there are 3 heads sides, 2 of which are the double headed coin.

A = See Heads
B = Pick two headed coin

P(A) = 2/3
P(B) = 1/2
P(A|B) = 1

P(B|A) = P(B)P(A|B) / P(A)  by Bayes's Thm
       = 3/4

AM I DOIN IT RITE?

>>5
damn it P(A) = 3/4 so final answer is 2/3

>>5

no, i'm still waiting for trolls and retards....

Lol. I was seriously scratchin mah' head for about 10 minutes here. Then I realised I read the question wrong. I thought the question was 'what are the odds that the OTHER coin is double-sided?' Which I'm pretty sure would actually be 1/2, strangely enough ;)

>>8

No, its 1/3

>>8 If that was true, then your original answer would be right anyway.

>>8 If that was true, then your original answer would be right anyway.

2/3 you have 25 % chance for tails 25% for headsnormalcoin and 50% for headsdoublecoin

You know its a head coin so 50%/75% = 2/3