1. The problem statement, all variables and given/known data Let ##100!=N\cdot 10^n##. If N is relatively prime with 10 and unit digit of N is d, then n+d is equal to A)26 B)28 C)30 D)32 2. Relevant equations 3. The attempt at a solution I don't think it would be a good idea to expand the factorial and separately write out the factors of 10. I have got no idea about how to approach this problem. Any help is appreciated. Thanks!