4. Neighbors (from 6th grade. 1 point). There are cards with natural numbers from 1 to 5. The cards are well shuffled and two are randomly selected. Find the probability that the numbers on the selected cards will be two consecutive numbers.
Solution. The total number of ways to choose two cards is $C_{5}^{2}=10$. There are 4 pairs of cards with two consecutive numbers. All combinations are equally likely, so the desired probability is 0.4. The problem can also be solved by enumeration.

Answer: 0.4.

![](https://cdn.mathpix.com/cropped/2024_05_06_435f41d051af721565ddg-04.jpg?height=363&width=422&top_left_y=912&top_left_x=286)