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Three people go into a restaurant and each of us has \$10. So we start with \$30.

The bill comes to \$25 which means there is \$5 left over. Out of that \$5 we each take back \$1 (which would be \$3 altogether), which leaves \$2 that we leave for a tip.

If we each took \$1 back that means we each only spent \$9 initially instead of 10. Now, 9 * 3 is 27, plus the 2 is 29. We started with \$30 so where did that other dollar go?

I've never understood this - I still don't know if I ever will but I'm just putting it out there to see if anyone else has found a way to understand it. I think it has been mentioned that it comes down to something like a decimal point (or something of that sort) but if it does then who spent more and how do we decide that? Just a little mind-boggle for the day :)

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    $\begingroup$ Welcome to Puzzling :) This question is similar to: Where has the last dollar gone?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. (PS This type of problem is often known as the 'Missing dollar riddle' - there's a page on Wikpedia that might help...) $\endgroup$
    – Stiv
    Commented Jul 6 at 9:55
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    $\begingroup$ The original 30 is no longer relevant, and each 9 includes the tip. So 9 * 3 = 27 minus the tip is 25. I think there is a similar deception that con-men play when asking for change of a banknote, and then change their mind about what they want part way through. $\endgroup$
    – Weather Vane
    Commented Jul 6 at 11:57
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    $\begingroup$ Also, this isn't "hard to explain" or "hard to understand". Someone is deliberately tricking you by acting like it's normal to add something in a place where you should subtract it, and comparing to an irrelevant amount, in order to make you feel like you "don't get it". $\endgroup$
    – Kate Gregory
    Commented Jul 6 at 15:08

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