#math trivia #126 solution

Every number divisible by 9 has a digit-sum that’s also divisible by 9.  For most small numbers divisible by 9, the digit-sum is exactly 9:  consider 9, 18, 27, 36, … .

The only day-numbers divisible by 9 whose digit-sum is not exactly 9 are 99, 189, 198, 279, 288, and 297.  This is a total of six day-numbers, so the answer is 40-6 = 34.

 

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