When dividing a whole number by a unit fraction, it can help to think of

how many times the unit fraction can fit into the whole number.

One way to divide 5 by $\frac{1}{3}$ is to think of it as, "How many $\frac{1}{3}$'s are in 5?"

First, represent 5 with a model.

Next, divide each whole into

$\frac{1}{3}$'s, which is the same as dividing each whole into three equal parts.

Then, count the number of $\frac{1}{3}$'s. There are fifteen $\frac{1}{3}$'s in 5.

So, $5\xf7\frac{1}{3}=15$.