I need some money for ice cream

Chris is in summer school for the next two weeks.  He came home Monday and told us that he needs money so that he can buy an ice cream during snack time in the lunch room.  I asked how much the ice creams cost.  He didn't know so I decided to send him with $2.  He came home and pulled out his change from buying his ice cream today.  He had a few quarters.  I asked again how much they cost.  He still didn't know but he said he gave them his dollar and they gave him some ice cream and some change.  So I ask where the other dollar is.  He says, "I traded it for another ice cream.  They'll let you have two, you know."