AIBUnreasonably stupid to not "get this"?

[Vilanelle]

Is this a riddle, or are my calculations bad?

"You see a £97 t-shirt but you don't have any money so you borrow £50 off your mum and £50 off your dad = £100. You buy the top and get £3 change, so you the decide to give your mum £1 and your dad £1 and you keep the other £1 for yourself. You now owe your mum £49 and your dad £49 so £49+£49=£98 and your £1 makes £99. Where is the missing £1?"

I can not work out where the other £1 is!

You have a 97 quid t shirt and £1 in cash.
You gave the other £2 to your mum and dad.
That's £100!

Oh dear lord. I get that straight away. Why didn't I click!?

Another version of this is here:

plus.maths.org/content/maths-minute-missing-pound

Interesting example of how making one false assumption can lead to a situation that doesn’t seem to make sense.

You now owe £98, that being the £97 item and the £1 you kept.

£97 item + £3 change = £97 item + £1 kept by you + £2 change to parents

Why would you add another £1 on to make £99? You’ve already counted it in the £98 you owe your parents.

Don't worry, my DH has explained a Saturday Guardian voucher system to me multiple times that I just can't get my head around.
Something about a £3 paper costing £2.50 (discounted rate due to voucher) but if he spends £10 at waitrose he gets it free anyway, so he's getting £13 of goods for £7.50....
Can't even explain it properly but every time he talks about it I think it's a waste of money and make him explain it again. He's actually drawn a diagram to explain it and saved it in our shared Evernote folder so I can refer to it when puzzled

Because the mathematics in the riddle is actually wrong. You owe your mum and dad 48.50 each for the t shirt plus 50p each for the pound you kept. So you do owe them 49 each, 98 total, as it says. But the pound you kept is included in that 98, not added on afterwards as they have said. That leaves the 2 pound you already paid him back.