How do you know if a girl is interested in you when she first sees you such as at a mall or or street dance?

if she looks at you with a smile, tries to show off after she sees you, or seems like she is paying attention, she probably is interested. if you think she probably is, go up to her and say hi, but don't give her some cheesy pick up line, she'll probably just hrow her drink at you. lol. but seriously, just say hi, if she smiles at you and says hi back or her friends kind of back up to leave you two alone (she probably told her friends you were cute) she likes you. and if she doesn't, then who cares, you're probably never going to see her again if you just met her at a dance or at the mall.

hope i helped!

p.s. dont ask for her number right away, ask as your leaving.
p.s.s. make sure she looks your age, it would be ebarressing if it were someone insanely older or younger than you