How many of the 200 smallest positive integers are congruent to 1 (mod 9)?
To be congruent to 1 (mod 9) means to have a remainder of 1 when divided by 9. The smallest positive integer that is congruent to 1 (mod 9) is 1 itself. The next one is 1 + 9 = 10, and then 1 + 9 + 9 = 19, and so on. I can see a pattern: the numbers congruent to 1 (mod 9) are those that can be written as 1 + 9k, where k is a non-negative integer. I want to find the largest value of k such that 1 + 9k is still among the 200 smallest positive integers. That means 1 + 9k ≤ 200, or 9k ≤ 199. The largest integer k that satisfies this inequality is k = 22, because 9 * 22 = 198 and 9 * 23 = 207. Therefore, the numbers congruent to 1 (mod 9) among the 200 smallest positive integers are 1, 10, 19, ..., 1 + 9 * 22, and there are 23 of them.

