Binary number interpreted as integer and you want 0 modulo 5, then we need 5 states. But as question is saying starting from 1, we add a new state which on input 1 will point to remainder 0 state of our mod 5 dfa and on 0 will go to dead state. So total 7 states.(5 states for mod 5 counting and 2 more for handling starting with 1 condition. )