For all the result-awaiting students (like me ) and all preparing for '15. here is something to get you engaged

A box contains 100 coins out of which 99 are fair coins and 1 is a double-headed coin. Suppose you choose a coin at random and toss it 3 times. It turns out that the results of all 3 tosses are heads.

What is the probability that the coin you have drawn is the double-headed one?