He borrowed $50.00 from mom and $50.00 from dad for a total of $100.00. He spent $97.00. He had $3.00 left. He gave $1.00 to mom, $1.00 to dad & kept $1.00 for himself. So now he owes $49.00 to each parent which adds up to $98.00. If you add the $1.00 he kept that adds up to $99.00. What happened to the hundredth dollar?