Three of them are unfair in that they have a 45% chance of coming up tails when flipped. The rest are fair. So for the rest of them, you have a 50% chance of tails or a 50% chance of heads. You randomly choose one coin from the bag and flip it four times. What is the percent probability of getting four heads? So let's think about it. When we put our hand in the bag and we take one of the coins out, there's some probability that we get an unfair coin.