I have two coins.
* One of the coin is a faulty coin having tail on both side of it.
* The other coin is a perfect coin (heads on side and tail on other).
I blind fold myself and pick a coin and put the coin on table. The face of coin towards the sky is tail.

What is the probability that other side is also tail ?

• ans is 2/3
  Let there be a good coin (1 heads 1 tails) and a bad coin (2 tails).
  
  The chances of you choosing each coin is 1/2. Since the probability of choosing the good coin is 1/2, given that tails is facing up, the probability of heads facing down would be 1/2*1/2 = 1/4.
  
  However, the probability of choosing a bad coin is 1/2, which means that the probability of tails facing downwards is 1/2. This is because no matter which tails is facing up, the other tails is facing down too.
  
  1-1/2-1/4=1/4. This 1/4 represents tails facing down and heads facing up. But this probability can be ignored in the context of the question because we know that tails and not heads is facing up.
  
  Given that tails is facing upwards, the probability of tails facing downwards would be (1/2) / (1/2+1/4) = 2/3
• 11 years agoHelpfull: Yes(2) No(0)
• ans =1/3
  there are three possibility {TT,TH,HT },
  so the posibility of tail on other side is 1/3
  
• 11 years agoHelpfull: Yes(0) No(0)
• ans=1/2
  one face of coin in already tail. so the other side can also b tail only when the faulty coin is chosen. so
  prob.=1/2
• 11 years agoHelpfull: Yes(0) No(0)