“I see a shirt for $97. I have no money, so I borrow $50 from my Dad and $50 from my Mom. I buy the shirt, then from the remaining $3, I give each of my parents $1 back. I now owe each of them $49, 49+49=98, plus the $1 I still have is $99, where is the missing money?”
I saw this question a while ago somewhere, but a friend of mine brought it up recently and I just can’t remember the trick to answering it. Help?
You have a shirt worth $97 and $1 = 98 dollars of value. You owe your parents 98 dollars, so you’re even, just like when you had no shirt and no dollars.
You originally owed them $100.
You game them $2.
You now owe them $98.
98 + 2 = 100
The one dollar in your pocket is irrelevant to the math.
Good explanations so far.
Here’s the Ask Dr Math FAQ on this problem (or a related variant, anyway).
Yeah, this is one of those math sleight-of-hand tricks. My initial reaction was:
"Adding the $1 in your pocket to the $98 you owe your parents is nonsense, because the $1 is part of the $98. You can subtract the $1 from the $98, and you have the money you paid from the shirt.
I gave this kind of answer to my grand-uncle. He paused for a bit and then retorted:
“So where’s the missing dollar?”
You can’t argue with logic like that… :rolleyes:
This is an example of a form of trick question. You’re given two sets of numbers that are independent of each other but close enough that the questioner can imply there’s a relationship. And then the questioner asks why when you add up the two sets of numbers they don’t come out the same. The answer is that there’s no reason for two sets of numbers to add up to the same amount.
Here’s a simple version to illustrate the point: If you multiply two and two together you get four. And if you add two and two together you get four. If you multiply two and three together you get six. But if you add two and three together you only get five. Where did the other one go?
The version I have heard most often is:
Three men share a hotel room for $30; each pays $10. The next morning, the hotel manager realizes the room rate should have been $25, so he gives $5 to the bellhop to give to the three men. The bellhop tells the men that the room rate was $27; he gives each man back $1, and keeps $2 for himself. Each man paid $9, and the bellhop has $2, but that’s only $29. Where’s the other dollar?
The “quick answer” to questions like this is, you’re adding things when you should be subtracting. In your original case, the $49 you owe to each parent is negative as far as you are concerned; it’s really -98, plus 1 for the dollar you have, plus 97 for the shirt you bought.
You borrowed ($50 from my Dad and $50 from my Mom) this is one transaction, not two. You borrowed $100.
You spent $97 and gave back two dollars. You still have the other dollar in your pocket. It goes back to (Dad/Mom).
This is why we use parenthesis in math equations.
This being the Straight Dope message board, it is obligatory to link to Cecil Adams’s answer.
Since illegal activities are disallowed at SDMB, please perform tricks like this only with play money.
Yes, because it’s not logic as we know it. 
The most I’ve ever spent on a shirt was around fifty bucks. The existence of a $97 shirt is what I’m stuck on here.
There’s no dollar missing.
The real trick is getting Mom and Dad back together again. 
And not sharing a hotel room with two men.
I tried this, but it didn’t work because my Dad spent his $50 on a zombie hooker.
So we are making zombie jokes even in fresh threads now?
Well, if people are gonna gripe at us for not seeing that a thread is a zombie thread, they kind of have to expect us to think that a thread is a zombie when it isn’t from time to time as well.
A $30 hotel room – that’s gotta come from a zombie discussion.