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counting and probability intermediate

Problem

If the six digits 1, 2, 3, 5, 5 and 8 are randomly arranged into a six-digit positive integer, what is the probability that the integer is divisible by 15? Express your answer as a common fraction.
Solution
By the fact that the sum of the digits is a multiple of 3, any arrangement of the digits will be a multiple of 3. To be a multiple of 5, the number must end in one of the fives, which will happen with probability . Since any number that is a multiple of 3 and a multiple of 5 is a multiple of 15, the probability of it being a multiple of 15 is .
Final answer
\frac{1}{3}