the only possible way (a-1)(b-1)(c-1) is not zero is if none of the dice have "1" on the face. There are the ways a=1 b=1 c=1 a=b=1 a=c=1 b=c=1 or a=b=c=1, and there are 216 total possible outcomes, so the answer is 216-7/216=209/207. (I may not have simplified)