A, B, C, and D represent different digits. AACA, ADDD, BCDB, and BDAC represent four different four-digit pri

Answer 1

Prime numbers, perhaps?

Then all four must be odd, since no even number greater than 2 is prime. And none of them can be 5, because any number ending in 5 has 5 as a factor. So they are 1, 3, 7, 9.

Answer 2

The first answerer is right. In addition it turns out to be 1,3,7,9 in that order.
ie A=1, B=3, C=7, D=9