You see a top you want to buy for $97, but you don't have any money so you borrow $50 from your mom and $50 from your dad. You buy the top and have $3 change, you give your mom $1,your dad $1, and keep $1 for yourself. You now owe your mom $49 and your dad $49.

$49+$49=$98 and you kept $1. Where is the missing $1?