how not to tip correctly

This has happened to me often enough over the years that I think there ought to be a name for it. Let’s say Person A and Person B go out for drinks together. A buys enough more stuff that they both feel splitting the check down the middle isn’t fair. Let’s say Person A drank $60 worth of stuff and Person B’s drank $40, for a nice round total of $100.

Person A wants to pay with a credit card and Person B wants to pay with cash. They got good service, and both want to tip 20%. B pitches in $48 in cash ($40 + $8 tip). Now the waitress takes B’s cash and A’s card back to the register and does the math. Since there’s $48 in cash, and the total bill is $100, the remainder for A’s card is $52.

Person A gets a credit card receipt for $52, and then adds on a roughly 20% tip - $10. He signs the credit card slip for $62.

Now the bar got $48 in cash and $62 on credit, for a total of $110. But that’s only a $10 tip on a $100 tab! What the hell happened? Both parties tipped about 20%, but now the waitress is only getting 10%!

Is there a name for this? How would you keep it from happening? (other than changing the premise that the two people don’t want to split the check down the middle)

In case you didn’t follow the math, here’s what happened that neither A nor B noticed (but you can be sure the waitress did).

Person A wasn’t paying close attention, and essentially pocketed the tip that B left for the waitress. B’s $8 tip went to reduce the bill for A’s drinks, and A didn’t notice because he’s not great at math or logic, especially after $60 of drinking.

What A should have thought is this: “OK, the pre-tip total was $100 and we should tip $20. So I’ll add that $20 onto my $52 credit card slip, for a total of $72. To double check, $72 + $48 = $120 = bingo!”