More exactly, it's been a long time since I've done much algebra, and it was a fight to get any sense out of problem. I had a feeling there was something I didn't understand, but I had no idea the weak spot was that the rounding off range didn't include the exact percentage.

Finding out how much a single vote changes the percentage of up or down votes gives a lot of information, and this can be learned by giving a vote and withdrawing it quickly.