4.1. A two-digit natural number $\overline{a b}$ is randomly selected from 21 to 45 (the probability of selecting each number is the same). The probability that the number $\overline{a 8573 b}$ is divisible by 6 is $n$ percent. Find $n$.
Answer: 16

Solution. There are a total of 25 options. The number $\overline{a 8573 b}$ is divisible by 6 if and only if both conditions are met simultaneously: $b$ is even and the sum of the digits $a+8+5+7+3+b$ is divisible by 3. Among the numbers from 21 to 45, the numbers $22,28,34,40$ (every sixth number) fit - this is 4 options. Therefore, the desired probability is $\frac{4}{25}$ or 16 percent.