Probability is simple. In this case, it's even easier.
Probability is the outcome. It's the outcome over a set amount of data under specifications.
Now, here you're given everything you need. This girl did 50 entries, each one involving three coin tosses. She grouped them per time, and put them in a list.
The specifics you're looking for is how many groups composed of 2 guys and One girl?
<span>The inverse image or preimage of a particular subset S of the codomain of a function is the set of all elements of the domain that map to the members of S. Image and inverse image may also be defined for general binary relations, not just functions.</span>