28. Write down a four-digit number where each subsequent digit is 1 greater than the previous one, then write the number with the same digits but in reverse order and subtract the smaller number from the larger one. Repeat this several times with different numbers and compare the results. Solve the problem in general terms. What do you notice?
28. Let the digits of the number $a, a+1, a+2$ and $a+3$, then one number is $1000 a + 100(a+1) + 10(a+2) + (a+3)$, and the number written with the same digits but in reverse order is $1000(a+3) + 100(a+2) + 10(a+1) + a$. Let's find the difference between these numbers: $1000 a + 3000 + 100 a + 200 + 10 a + 10 + a - 1000 a - 100 a - 100 - 10 a - 20 - a - 3 = 3000 + 200 + 10 - 100 - 20 - 3 = 3087$. As we can see, the difference under the given condition of the problem is always 3087.