Originally posted by garethnLooks good to me.
A, B, C and D represent four different digits such that ADDD, AACA, BCDB and BDAC are prime numbers.
What digits do the letters represent?
Each digit is odd since each of the four primes expressed above ends in a different digits A-D.
No digit is 5, since any number ending in 5 is divisible by 5.
So the four digits are 1,3,7,9
We find that A=1, B=3, C=7, D=9
giving 1999, 1171, 3793 and 3917 as the primes