Example 1. In an urn, there are 10 balls of the same size and weight, of which 4 are red and 6 are blue. One ball is drawn from the urn. What is the probability that the drawn ball will be blue?
Solution. Let the event "the drawn ball is blue" be denoted by the letter $A$. This trial has 10 equally likely elementary outcomes, 6 of which are favorable to event $A$. According to formula (1.2.1), we get

$$
P(A)=\frac{6}{10}=0.6
$$