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 ?

2/3

2 possible scenario are :

case number side shown other side

1 A1 (H) A2 (H)

2 A2 (H) A1 (H)

3 B1 (H) B2 (T)

4 B2 (T) B1 (H)

case 4 is not possible so ans is 2/3