This math problem is a real twister; I've been thinking about it for half an hour and still can't solve it.

twister 是由动词 twist（扭曲、缠绕）加后缀 -er 构成的名词，字面意思是"扭曲的东西"。在这里用作比喻，表示"令人困惑、难以解决的复杂问题"，类似于中文里用"绕弯子"来形容难题。