I got this puzzle that I need help on. I hope its not too easy because I really don't understand it.
A bag contains 100 coins. 99 of them are fair and will give heads or tails with an equal probability. 1 biased coin will always yield heads. I pull a coin out randomly from the bag and toss it up 3 times. In each of the 3 times it lands on heads.
What is the probability that I pulled out the biased coin?