when you are out in a group at a bar or restaurant and there is a shared bill and no one has change(usually for a twenty) or the correct amount for their portion of the tab . Thus follows a complex series of illogical but correct money swaps to come out with the correct amount for the bill plus tip.
Lets settle the bill. I think we need some table math. You give me a twenty, i will put in fifteen and cover you five on your tab and then you give him a ten. That should make us even.