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Since the number is between 300 and 400 this would mean that the hundreds digit is 3. We let the two other digits be b and c.

3 + b + c = 5(3)
b + c = 12

Since c is odd and b and c range from 0 to 9 the only ordered pairs for (b,c) are:
(9,3), (7,5), (5,7), (3,9)

Since we can't repeat digits the remaining pairs would be:
(7,5), (5,7)

The only numbers possible would be 375 and 357.
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