"I am a girl, and you?"
Translation:Я девочка, а ты?
It seems a bit strange to me to use the informal ты with someone (presumably a correspondent) whom you do not know well enough to know the gender of! Is this because if I am a девочка I must be a child, and am speaking to another child? Would a single female adult ever decribe herself as a девочка?
I used и in this sentence as it seemed it could go either way between this and а, given the question. If the "девочка" doesn't know whether to expect that the other person is a boy or a girl, why does it matter which conjunction is used - unless she is expecting the other person to be a boy, in which case there's no need for the question - ?
No, because тебя is accusative and the nominative is needed here. The implied sentence is "I am a girl, and/but you are a boy/adult/alien." So "you" is the subject of the second clause (and the verb is omitted because Russian does not use a present tense of "to be"). Hence "you" needs to be in the nominative case, which is ты.