A: Only under certain circumstances:

In the current version (Math 2.0) when playing with the Math Rules Meta Rule (orange stripe), it must be your turn to claim victory. In Math Fluxx 1.0, the same conditions occur when either of the three Victory Rules are in play: Times Victory, Plus Victory, or Combo Victory.

No matter which version you have, the situation is really the same: if you have to use math to get your Keepers to make the number on the Goal, then the idea is that it’s really mentally taxing to have to be watching and constantly recalculating to know whether you can jump in and declare a win. Instead, you only have to assess the Goal which is there on your turn, to see whether you can win with math.

This doesn’t mean you should just relax your math-brain between turns, however – it really helps speed the game along if you have your calculations all figured out when your turn comes. But remember – if you do realize you can win via math when a Goal is played, but it’s not your turn, it’s probably best not to mention it until your turn rolls around, or else someone may make a point of changing it before it’s your turn again.