Stupid Is as Stupid Does

1. My dad has a knack for justifying any purchase by using math.
2. I skipped three years of grade school.

We're at the Disney Store and I'm debating a purchase for my girls (ages two and four) for Christmas. It's an $80 dollhouse and I don't know whether to buy one or two since they don't always share well.

Dad: Let's assume [4yo] is at home for at least another nine years if she goes to college at fourteen like you did. So that's less than ten dollars a year for the dollhouse. And if [2yo] is home for another eleven, that's a total of twenty years of use, so that comes out to four dollars a year. Now, if they're stupid and don't start college until they're eighteen then you're looking at thirteen and fifteen years, so that's. . . less than three dollars a year for one dollhouse, just under six for two of them. Though, granted, that's if they're stupid and if they use them the whole time they're home.
Mom: And they'd have to be really stupid to play with dollhouses that long.