How many positive multiples of 3 less than 1000 use only the digits 2 and/or 4?
We can list them since we know that a multiple of 3 has to have a digit sum that is divisible by 3:
24
42
222
444
That's it... So we have 4 positive multiples of 3 less than 1000 using only the digits 2 and/or 4.
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