An urn has 6 balls numbered from 1 to 6. If two balls are drawn, what is the probability that the difference between the numbers on these 2 balls is 1?
Let's observe that if we extract the first ball with a number between 2 and 5, then among the 5 balls that remain in the urn, there are two possible balls that meet the condition of the problem. Therefore, in this case, the probability that the second ball meets the condition is $\frac{2}{5}$, and the probability that the first ball has a number between 2 and 5 is $\frac{4}{6}$. On the other hand, if the first ball extracted is 1 or 6, we only have one ball in the urn that meets the condition, so in this case, the probability for the choice of the second ball is $\frac{1}{5}$, and the probability that the first ball is 1 or 6 is $\frac{2}{6}$. Therefore, the probability that the balls are consecutive is

$$
\frac{4}{6} \times \frac{2}{5}+\frac{2}{6} \times \frac{1}{5}=\frac{1}{3}
$$