Find the probability of getting one tail and three heads when you flip a fair coin four times.

Well, when you flip a coin, there's a 50/50 chance it's going to land on heads or tails. so if you flip a coin 4 times there's a small chance it's going to be on heads and three tails.
some probabilities are-
-all four heads
-all four tails
-two heads two tails
-3 heads one tail
-1 tail 3 heads
so, therefore there is a 1/5 chance that it is going to be one heads and three tails. I hope this helps

Set up a system of equations