Little explorations with HP calculators (no Prime)

[Csaba Tizedes]

1.) My first thought was that, where is the puzzle? This is simply wrong - because C+CC=D8, not D4!
2.) OK, which BASE is that where this will be OK? If we assume that the digits are marked with the English alphabet, it's simply to calculate in base=20 the above addition will be right: C+20×C+C = (12)+20×(12)+(12)=264 and 20×D+4=20×(13)+(4)=264, so it is OK.
3.) Also, as per original quiz, as I can see we must to solve (C)+(C)×b+(C) = (D)×b+(4), and we are searching for C, D digits and b base.
4.) In base b=10, the solution is C=7 and D=8

Csaba