The One Dollar
Three friends go for coffee and biscuits. The bill total comes to $25. Each take out a 10$ bill. The waitress brings back five $1 bills as change. Each friend keeps one $1 bill and the remaining $2 dollars are given as tip.
Now, each friend gave a $10 bill and took back $1 effectively giving $9. Three friends makes it $27 dollars in total given. And the tip was $2 which sums it up to $29. Where is the missing dollar ?