Try to solve this...

There were three guys at a bar, and they had to pay $30, so they paid $10 each..

so $10+$10+$10 = $30

But hey... there was a mistake, they had to pay $25 instead of $30 actually, so they got five $1 coins back and they leave a $2 tip.

So here's the thing: Everyone payed $10, minus the $1 they got back, it's $9 each, so $9x3 = $27 + the $2 tip it's = $29, but in fact they payed $30... so where's the missing $1?

Solve it and you might just get that $1.

I finally found the missing $, the poster swallowed the coin and not survived the operation to retrived it. RIP