When we multiply a whole number with a fraction, we can think of the whole numbers as "over one"...
5 3 5 15
3 * --- = --- * ---- = ----
6 1 6 6
We can further simplify the fraction, by dividing numerator and denominator by 3...
15 15 / 3 5
--- = ------- = ----
6 6 / 3 2
Since this is an improper fraction, we need to turn it into a mixed number...
5 2 + 2 + 1 2 2 1 1 1
---- = -------------- = --- + ---- + --- = 1 + 1 + ---- = 2 --- or 2.5
2 2 2 2 2 2 2
