Example 1. From the five numbers $1,2,3,4,5$, take out three numbers, find the probability that the sum of these three numbers is divisible by 5.
Analysis: $n=C$ Using the enumeration method of combinations, we can get that the possible cases for three numbers being divisible by: 5 are $(1, 4, 5)$, $(2,3,5) . \therefore \mathrm{P}=\frac{2}{10}=\frac{1}{5}$.