"Would you like a beverage for the remainder of your flight?"

As I sat on the flight making small talk with the man sitting next to me, the stewardess began serving us drinks. The man in front of me ordered a drink costing $4.00. At the time she didn't have $16 to return to him so she said she'd be back with his change. Over the intercom they made an announcement asking if anyone had change for a $20. She had 2 tens, but she needed a ten, a five, and five one's in order to give him the proper change. Little math nuances like that pop up everywhere!