Problem 4. In an urn, there are 10 balls, among which 2 are red, 5 are blue, and 3 are white. Find the probability that a randomly drawn ball will be colored (event $A$).
Solution. The following outcomes are possible: $E_{1}$ - a red ball is drawn, $E_{2}$ - a blue ball is drawn, $E_{3}$ - a white ball is drawn. The number of all possible outcomes is equal to the number of balls, i.e., ten, $n=10$. Of these, the number of outcomes $E_{1}$ is two, $E_{2}$ is five, and $E_{3}$ is three.

All ten outcomes form a complete group, i.e., they are equally likely, and only one ball is drawn. Therefore, these ten events are elementary, of which seven are favorable for event $A$, namely two events $E_{1}$ and five events $E_{2}$: $m=7$. Consequently, by formula (1) $p(A)=\frac{7}{10}=0.7$.

Answer. $p(A)=0.7$.