[Math] Amount of odd-digit numbers divisble by 3

elementary-number-theory

I encountered the following problem for homework- An "oddie" is a 3 digit number with all 3 digits odd. How many "oddies" are divisible by 3?

There are 125 "oddies" and 300 3-digit numbers divisible by 3, but I still have no idea how to solve this. Please give me a hint or something to start me off with.

Best Answer

Hint: is there a way to check that a number is divisible by 3, based on its digits?

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