I went to a Mexican restaurant and this is how my conversation went:
Yo: Quiero un vaso de agua de sandía.
Camarera: ¿Chica o Grande?
Why did the waitress use "chica" instead of "chico"? Isn't she asking me how big of a cup I want? Cup is masculine, so I would presume that the adjective describing it should also be masculine. The waitress also used the same feminine "chica" with the next customer, so I doubt she botched up the word.
In general, how do you decide on the gender of an adjective when its noun is implied?