Now, we know from our previous consideration that there are five ways in which the number of heads could be one. 5!/4! 1! happens to be 5. We also know that there are 32 possible outcomes. It is 2⁵=32 outcomes. This is the size of a truth table. So, 5 out of 32 outcomes has exactly 1 head. So, I would suggest that the answer is 5/32, and my calculator tells me this is 0.15625. So, that is actually interesting. If you flip a coin five times, there’s a chance that it only comes at head exactly once and that is the probability 0.15625.