If you are meeting a woman regularly in a public place, like night school,

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a local bar, recreational sports...? ... and you are attracted to her and you feel she is attracted to you, should you ask her out quickly or should you take your time? How long is too long until you ask her out or ask for her phone number? Will she get scared if you ask for her phone number too soon?
Mmmmm? .... I was told that I should never give a girl my number because it makes it seem that I just want sex. Where as if I ask for her number it shows that I really want to talk.