Thanks, sunny! (Actually, the math is wrong in my example, but I'm too lazy to go back and correct it--and it wouldn't change the point I was making, anyway.
I agree with Nikki and essarge that starting out cautiously with 1 card is a good way to establish credit. My point is that for someone who A)doesn't seem to have a good basic understanding of how credit works and how it should be used (I
sure didn't, at 18!) and B)doesn't have enough money in savings ($300 is the usual amount) to put towards a security deposit, is someone who needs to educate herself about credit and put some $$ aside before getting that piece of plastic.
Miss JKm, I hope you are taking everyone's advice in the spirit it's being offered. Many of us have made silly, stupid and certainly expensive credit errors when we were younger. Benefit from the wisdom of our mistakes and don't get into a crippling financial mess when you're just starting out.