Decimal Diner is a fun, real-world math activity where students practice adding decimals and calculating percentages. Students select food items from a menu, add up the total cost of their order, and then determine the tip at three different percentages: 15%, 18%, and 20%. Finally, they calculate the grand total (meal + tip). This activity helps students strengthen their skills with decimal operations, percentages, and real-life money math in an engaging, restaurant-themed setting.