You should never put any information which might give away the kata solution in the comments (without checking the "mark as having spoiler content" box) as they're visible to every one.

Thanks, it's just because I'm new to coding. I realised after completing this challenge. That was a leftover from other code I had been trying.

Range has a #sum method, which will cover the 0 case on its own: (1..num).sum works perfectly