1117 = 710 ?
I'm sorry. I know this question is for @Momgie but I can't help. >.< I just want to share my guess.
In 1112 = 25, the first digit of the answer, '2', refers to the last digit of the question, which is '2'. And the last digit, '5', is the sum of the digits of the question, which is 1+1+1+2 = 5. The remaining examples are just like that.
That was just a guess.