There are eight different possibilities for outcomes of three tosses:
1. Head, Head, Head
2. Head, Head, Tail
3. Head, Tail, Head
4. Head, Tail, Tail
5. Tail, Head, Head
6. Tail, Head, Tail
7. Tail, Tail, Head
8. Tail, Tail, TailThe 8th possibility will not give us at least 1 head so we will cross that one out. So there is a 1/7 possibility for at least 1 head.