The price for the breakfast is $20 and they took in $253. That means they had 12.65 people in attendance. Now, if they made $20.20, that means there was an average profit of $1.60 per person or a margin of 8%.

If the actual price of the meal is $8.76 including tax and tip then the profit should have been $11.24 per person for a margin of 56%.

So what happened to the missing 48% of the profits? There can be several explanations: a) Maybe Bob is a really big tipper, b) maybe he is a really awful negotiator, c) maybe he is really bad a math, or d) maybe his numbers are not quite accurate.

I can't see how he had to "chip in", though.

Unless he was playing golf when he was doing his calculations.