I have two questions about expressions of number of people in Russian:
Once when buying tickets at кассы, I heard the expression "три взрослых". I thought with numbers 2-4, we use the genitive singular form. So why is it not "три взрослого" here?
Another time when me and my friends entered a restaurant, I heard the waiter say "четверых", which I guess is the genitive form of "четверо". Can anyone explain to me why we use the genitive case here?