Posted by tyler on Tuesday, November 8, 2011 at 7:51pm.
we know that the number is 3xx
the tens digit is either 1,4, or 9
4+3 =7 is a prime, so the number is 34x
x cannot be 2 or 5, because 342 and 345 are divisible by 9 (cast out nines)
The number must be even, because it is divisible by 4. So, it is either
340 344 346 348 (but 4 does not divide 346)
Only 348 is divisible by 3 (cast out threes)
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