Question

Famous Probability Interview Problem
James Horner is having two coins in his hand. Out of the two coins, one is a real coin and the second one is a faulty one with Tales on both sides. He blind folds himself choose a random coin and tosses it in the air. The coin falls down with Tale facing upwards. What is the probability that this is the faulty coin?

Answer 1

2/3

While tossing the coins in this case only two cases are favorable:

1) A1 (H) A2 (H)

2) A2 (H) A1 (H)

3) B1 (H) B2 (T)

4) B2 (T) B1 (H)

Since the fourth case is not feasible, the probability is 2/3.