Writers are really bad at maths. Any standouts exemples?

When you niptick on details like population size, distance or timeline. A lot of times you realize writers don't really realize how math works.

And then sometime you have things like Avatar:TLA having be forced to justify Kyoshi having lived for 200 years because the writers confirmed she was the one just before Roku but then realized the giant gap in the timeline.

Most of the time it's not too story breaking but it can still be a bit weird you think about it.