Weighted averages tend to be a topic reserved just to education and grading. This quick self-teaching lesson and practice problems shows students how weighted averages can extended into their every day lives with validating credit card numbers. In this mini-lesson, students will learn how digits in a credit card are given weights and then added together to reach a value that ends in a zero using the Codabar method. Students will complete two problems to determine if a given credit card number is valid. They will also learn how the last digit in a credit card number is a check digit that is only there to ensure the total weighted value ends in a zero. Students will calculated the check digit value needed to create a valid credit card number. If you like this product, also check out my Barcodes and UPCs Weighted Average for another related topic. Detailed answer key is included. This mini-lesson takes between 20-30 minutes depending on your students. I use it for my Discrete math students, grades 11-12, as an independent exploration.