In an opaque bag, there are $5$ red balls, $5$ white balls, and $5$ yellow balls. The balls are the same except for their colours. Take out one ball from the bag. What is the probability that you take out a yellow ball? 
Overseas Competition->Knowledge Point->Counting Modules->Statistics and Probability->Questions Involving Probability->Basic Concepts of Probability
$\dfrac{5}{15}=\dfrac{1}{3}$. 