There are two ways to figure this. Since there are only four possible outcomes for tossing two coins, you can simply enumerate them and count the successes.
Failure: 2 heads Success: 1 head Success: 1 head Failure: 0 heads
Two successes out of four possiblities. Probablity is 1/2.
Or you can get fancy and use the formula for the probability of successes in trials where is the probability of success on any given trial:
Where is the number of combinations of things taken at a time and is calculated by
Or for your problem:
John
My calculator said it, I believe it, that settles it
