You see a shirt for £97, but
You don't have the money, so you borrow £50 off you're Mum and £50 off you're Dad.
£50+£50=£100, right?
... ...
You buy the shirt and have £3 change, you give £1
to you're Mum, £1 to you're dad and you keep £1 to yourself.
I still don't get it. If you borrowed £50 of your Mum and Dad for a shirt and the shirt costs £97 why didn't you just give them £1.50 each and it would save all the confusion :-)
There is no missing pound:
"You buy the shirt and have £3 change, you give £1 to your mum, £1 to your dad and keep £1 to yourself" <-------- CORRECT
"Now you owe them both £49" <--------- CORRECT
£49 + £49 = £98 + YOUR £1 = £99 <-------- WRONG
You are £98 in debt (£49 each to your mum and dad) and you have £98 worth of goods (a shirt worth £97 and £1 in cash) - everything balances as it should.
Some joker glued it to the pavement but my brother had the last laugh. He got a hammer and chisel from his van and hammered it off the pavement (true story).