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.

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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.