There are variations of the "missing dollar" riddle. The one I heard about 15 years ago (from a Clevelander named Randy) went like this:
3 guys get a hotel room, pay $10 each, total cost = $30.
The manager decides to refund $5, gives the $5 to the bellboy to return to the guests.
The bellboy decides to keep $2 for himself...gives each guest back $1.00
Each man paid $10, then was each refunded $1, meaning they paid $9 per person.
$9 times 3 guys = $27 + the $2 the bellboy kept equals $29. ...where did the missing dollar go???
It's a misdirection...the ONLY reason the guys paid $27 is because the bellboy kept $2 for himself. (You don't "add" $2 to the $27 to balance the equation.)
The real breakdown goes like this:
$30 minus $5 refund = $25 total cost to the guests. The bellboy takes $2 for himself = $27 total cost to the guests (or $9 each) Add the $3 that was refunded to the guests and all $30 is accounted for...nothing is missing.
By the way, Randy (just slightly inebriated at the time) refused to listen to a word of it. "OH YA, RIGHT! Youuuu figured it out...it's a mathematical mystery dude...the dollar is gone man, it's gone!!!"
--Such is the fun of getting into an argument with a guy at a bar when you’re not drinking and he is. :-)