Grandpa is visiting his cousin Bob. They go to a nice Restaurant for Lunch. The food and service were great. Waitress was charming. She brings the bill. It is 22 dollars. Bob says to Grandpa "I will pick up this tab". 

He puts exactly 30 dollars with the bill in the tray. The waitress comes and picks up the bill and the money, looks at it. She is not happy. Bob and Grandpa get a nasty look from her.

For the dinner they go to another Restaurant in the nearby town. The service was bad. The food came very late. The waitress was grumpy. She finally brought the bill. It was 67 dollars. Unhappy Grandpa said: " I will take it". 

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> He puts exactly 67 dollars in the bill tray. They both walk out. The waitress comes running out of the Restaurant with the bill tray and money in her hand. With a big smile on her face she says: "Thank you so much!". 
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What happened?