You see a ?97 shirt, but don't have any money, so you borrow ?50 from your mum & ?50 from your dad = ?100. You buy the shirt and have ?3 change, so give your mum ?1, give your dad ?1 & keep ?1 for yourself. You now owe your mum ?49 & your dad ?49. So.. ?49 + ?49 = ?98 & your ?1 = ?99. So where is the missing ?1?
