Can anyone help me answer this?..
You see a shirt for £97, but you don't have any money.
You borrow £50 from your mum, and £50 from your dad, so you have £100.
You buy the shirt, and have £3 change.
So you give your mum £1, your dad £1 and keep the other £1.
You now owe your mum £49 and your dad £49.
£49 + £49 = £98 and your £1 makes £99.
Where is the missing £1?
Think of it this way:
Your debt is 100 pounds combined. After giving back 1 pound to your mom and 1 pound to 1 dad reduces your debt by 2. So now your debt is 98 pounds. That means that any number of pounds you have with you can only be used to reduce the debt, and not to increase it. In terms of mathematical operations, the number of pounds you have with you can only be subtracted from the total debt, not added to the debt. The one pound you are left with can only be used to reduce your debt by one, meaning it cannot be added to 98 to get the result 99, but only subtracted from 98 to get the correct answer 97. Get it?
Nothing is missing, you are just forced into paradox by the incorrect operation performed between the debt of 98 pounds and the one pound you have with you.
I hope nothing is lost in translation since English is not my native language.