Maths riddle. Wrecking my head.

[Stvoider 10]

Anyone know how to solve this?

 

You see a shirt for £97, you can't afford it so u borrow £50 from your mum and £50 from your dad which equals £100. You buy the shirt and get £3 change so you give your dad £1 and your mum £1 back and you keep the other pound. So now you owe your mum £49 and dad £49, 49+49 =98 + your £1 =99. Where's the missing £1?

[HeadingNorth 11]

There is no missing pound. The addition of the two sums you owe to the pound you still have is nonsensical; but because the riddle is designed to make that nonsensical addition come out at very nearly the correct amount (£100) it fools people into thinking it should make sense.

[Alcoblog 10]

Erm ... did you drop it in the shirt shop?

[Stvoider 10]

There is no missing pound. The addition of the two sums you owe to the pound you still have is nonsensical; but because the riddle is designed to make that nonsensical addition come out at very nearly the correct amount (£100) it fools people into thinking it should make sense.

 

Indeed. But it all makes sense until the end

[Stvoider 10]

Erm ... did you drop it in the shirt shop?

 

No. But I think I'm starting to find out where my spare money goes.

[danot 10]

Anyone know how to solve this?

 

You see a shirt for £97, you can't afford it so u borrow £50 from your mum and £50 from your dad which equals £100. You buy the shirt and get £3 change so you give your dad £1 and your mum £1 back and you keep the other pound. So now you owe your mum £49 and dad £49, 49+49 =98 + your £1 =99. Where's the missing £1?

In your pocket.

[flamingjimmy 10]

Anyone know how to solve this?

 

You see a shirt for £97, you can't afford it so u borrow £50 from your mum and £50 from your dad which equals £100. You buy the shirt and get £3 change so you give your dad £1 and your mum £1 back and you keep the other pound. So now you owe your mum £49 and dad £49, 49+49 =98 + your £1 =99. Where's the missing £1?

 

There is no missing pound.

 

You've already paid back 1 pound each to your parents so the total debt should only add up to 98, and it does.

 

You owe your mum £49 and your dad £49 and you have 1 pound + a shirt.

 

The '+ your £1' bit is the part in there to confuse you.

 

EDIT: Dammit HN! Ninja'd!

Edited September 13, 2011 by flamingjimmy

[boyfriday 21]

You should have paid them £1.50, not a £1 each

[Stvoider 10]

You should have paid them £1.50, not a £1 each

 

I know, but I wanted a pasty.

[HeadingNorth 11]

Indeed. But it all makes sense until the end

 

That's why it successfully confuses people. Everything up until the last addition is perfectly valid, and therefore you're pre-conditioned to assume that the last addition will also be valid. It isn't.

 

There are two valid ways of adding sums together; the £97 you paid for the shirt, the pound you gave to each parent, and the pound you still have: 97+1+1+1=100.

 

Or, the two lots of £49 you still owe, plus the two pounds you already paid back: 49+1+49+1=100.

 

Adding together two sums you still owe to a sum you still have left gives a meaningless total, but one which - thanks to the design of the riddle - is close enough to 100 to make you think it should actually be 100. In fact it could be absolutely anything. Write out the riddle with a shirt price of £83 and borrowing two fifties, and see what you get.

[Alcoblog 10]

Anyone know how to solve this?

 

You see a shirt for £97, you can't afford it so u borrow £50 from your mum and £50 from your dad which equals £100. You buy the shirt and get £3 change so you give your dad £1 and your mum £1 back and you keep the other pound. So now you owe your mum £49 and dad £49, 49+49 =98 + your £1 =99. Where's the missing £1?

Hang on ... so you've got a quid left, even though one's gone missing?

If you give your ma and pa 50p each of that quid, you then owe them each£48.50. Add that together and it comes to £97 ... you've got nothing left, so where's the £3 gone to!?

[boyfriday 21]

I know, but I wanted a pasty.

 

Where can you get a pasty for a quid, without losing the shirt off your back?