よ and の used differently

Hmm.. my japanese friend (dunno if it matters, but she's from Tokyo) constantly says these.. but I don't understand well.. and I never taught the particles used this way:

eg: 痛いの？ 良いの？ 眠いの？

WHy is there a "no" at the end? Is the meaning... does it hurt, is it good? She uses it for many things, very constantly.. but why "no"? I was taught maybe... to use でしょう? ね? ですか? か? Can you help me understand?


eg: 1: 大丈夫？
2:良いよ.

So... "ii yo" Is "it's good" "it's fine" "I'm fine"? Can you use this more often? When? Instead of "daijoubu da yo" or something like that? I'm not really sure if you can or not...

Hmm..

~Kisu

The の is the affirmation suffix without the copula (です/だ). It would be the same as saying 痛いのですか, 良いのですか, and 眠いのですか, respectively, except not as polite. Usually when the copula is omitted, it means plain speech.