Two deaf and dumb guy Rooney and Rojo went to the train station. Tickets for the train is 1/2 dollar i.e 50cents. Rooney gave the ticket booth guy a dollar and without even looking at him, he gave Rooney two tickets.

How does ticket booth guy know that they need two tickets and now one?

Because Rooney gave the ticket owner 4 quarters which only implies that they need two tickets.