If 5 coins are flipped what is the probability of getting only one head? How would I do this question? I know if the question said: at least one head then I would do:
${5\choose0}=1$
$2^5=32-1 = 31 $

We assume that the coin is fair and is flipped fairly.
There are $2^5$ equally likely strings of length $5$ made up of the letters H and/or T.
There are precisely $5$ strings that have exactly $1$ H and $4$ T.
So the required probability is $\dfrac{5}{2^5}$.
Remark: Suppose that a coin has probability $p$ of landing heads, and $1-p$ of landing tails. If the coin is tossed independently $n$ times, then the probability of exactly $k$ heads is $\binom{n}{k}p^k(1-p)^{n-k}$.
In our case, $n=5$, $p=1/2$, and $k=1$. 
