Is 几个 used for countable nouns and 多少 used for uncountable nouns?
几个 is used for small numbers and 多少 for larger numbers. In general 几个 is use when the answer would be 10 or less. Look at the tips in Payment and Time-1.
你们有。。。not accepted. How exactly are people expected to know if it's singular or plural you?
I think 个 is not necessary. Will a native speaker clarify.
I didn't add the 个and was marked correct, so it must be acceptable.
I did not add the 个 and was marked incorrect.