Saturday, March 18, 2017

The Extra Dollar

Here is an old math puzzle that you can find many versions of online.

Two friends have a meal at a restaurant, and the bill is $25. The friends pay $15 each, which the waiter gives to the cashier. The cashier gives back $5 to the waiter. The friends tell the waiter to keeps $3 as a tip, so he hands back $1 to each of the two diners.

So, the friends paid $14 each for the meal, for a total of $28. The waiter kept $3, and that makes $31. Where did the extra dollar come from? Give yourself a moment to think about it before clicking below for the solution.


Tim Kington said...

That's one of my favorites. My dad's math teacher in middle school told it to the class as an example of "one of those times when math just doesn't work".

Bill the Lizard said...


It's definitely a tricky one. I've seen lots of variations on this problem, and I used to get tripped up on them all the time. At some point I learned the trick to them, which is to look for the amount that's being counted twice. (In this case, the tip.)