So.. You want to but a shirt that costs £98. Bad news, you can't afford it this month. So, you borrow £50 from mum and £50 from dad to make a total of £100. You then buy the shirt and have £3 change. You decide to split the money and give £1 to your mum, £1 to your dad and keep the last £1. You now owe both your parents £49. BUT 49 49=98. Plus the £1 you kept to yourself which gives you a total of £99. But where did the last £1 go?