How to ask girl for number? In my Chinese class we haven't really discussed how to ask people for their number, only business cards "Zhao pian" what would be the proper way to ask a girl for a number? I am thinking "wo keyi you shu" with the vocabulary that I do know.
I assume you want ask number for dating purpose. 

I don't think this is a Chinese language problem. The difficulty is not how to ask but when to ask.

"number" should be translated into "号" but not "数" here.

You may say "我能留一下你的手机号吗？"(May I take down your phone number?). However, the more popular way in China is to ask their to add your WeChat(http://www.wechat.com/en/).