Dining Hall Chairs

so my friend and i were sitting at a table in the dining hall, and behind us was a table of three people.

and at some point while we're eating, these three people leave, and 2 girls come and sit down there.

and we get up to go get some more food, and when we come back there is an extra chair at our table, and the table behind us has only 2 chairs.

so doing the difficult math of 3-1=2 and 2+1=3, i figure that these 2 girls just decided that they didnt want an extra chair and decided to just put it at our table. luckily, they were in earshot to hear our whole conversation about where the chair had come from, that it had very obviously come from their table, and they were probably really weird.

awesome..