When we go out to eat at a restaurant, it’s customary to tip as a percent of the bill. What this means, though, is that the tip doesn't depend on how hard the server works, but how expensive the menu is.

In this lesson students will use mental math to quickly estimate tips – 10%, 15% and 20% – at various restaurants. As they do, they’ll realize that the pricier the food, the larger the tip. Students discuss whether they think this is fair, and come up with alternative methods of tipping.

### Students will

• Understand that “per cent” means “for every 100,” i.e. a 20% tip means \$20 for every \$100 worth of food
• Given a restaurant bill, use mental math to calculate three common tip amounts: 10%, 15% and 20%
• Use the Distributive Property to justify that tipping on individual items is the same as tipping on the total bill
• Understand that tipping as a percent, servers are compensated on the relative cost of the menu
• Compare different methods of tipping and create and justify their own

### Before you begin

Students should know how to calculate a percent of a given number. They will be using mental math to calculate common percents (multiples of 5%), so it will be helpful if students are able to find 10% of a number without the use of a calculator, to use as a benchmark value. To the extent possible, we recommend putting the calculators away for the duration of this lesson.