have one's number 对某人心中有数
【讲解】
名词number指的是“数量，总数”，have one's number 则指“对某人心中有数”，尤其指“对某人的能力或性格心中有数”。
【对话】
A:I was wondering if you could give me a day off.
A:你能不能给我一天假？
B:What for?
B:为什么？
A:I'll have to rewrite my thesis. That'll take much time.
A:我得重新写论文，那要花很多时间。
B:Stop trying to fool me. I have your number.
B:别想糊弄我，我清楚你的底细。
