If you want to know what the probability is to get at least one Heads, then that is the same as the probability of all the events (100%, or 1) minus the probability of getting all Tails.
There are 100 coins. 99 are fair, 1 is biased with both sides as heads. With a fair coin, the probability of three heads is 0.53=1/8. The probability of picking the biased coin: P(biased coin)=1/100.
