Example 19. On 30 identical tokens, 30 two-digit numbers from 1 to 30 are written. The tokens are placed in a bag and thoroughly mixed. What is the probability of drawing a token with a number that is a multiple of 2 or 3?
Solution. Let's denote the events: $A$ - "a token with an even number is drawn", $B$ - "a token with a number divisible by 3 is drawn"; $A B$ - "a token with an even number divisible by 3 is drawn". We need to find the probability of the event $A+B$. Since $A$ and $B$ are compatible events, then

$$
P(A+B)=P(A)+P(B)-P(A B)=\frac{15}{30}+\frac{10}{30}-\frac{5}{30}=\frac{20}{30}=\frac{2}{3} \approx 0.667
$$

(Event $A$ is favorable in 15 elementary outcomes, event $B$ in 10 outcomes, event $A B$ in 5 outcomes).