The wonders of maths

You want to buy a shirt that costs 97 pounds. You don't have the  money so you borrow 50 pounds from your mum and 50 from your dad. 50+50=100
You buy the blouse and you have 3 pounds left. You give your mum 1 pound and your dad 1 pound and you have 1 pound left for yourself. You still owe your mum and dad both 49 pounds.
49+49+1 (pound that you have)=99
Where has one pound gone?