Credit Cards & Recursive Geometric Formulas

This is my first lesson post with materials, so please comment if you need more information, or if things don’t work.

Learning Targets:
1. Students will be able to write a recursive formula with a percent increase or decrease.
2.  Students will know how a credit card balance is calculated (hindsight:  they need to know how a credit card works)
3.  Students will know about credit card fees, APR, interest and monthly payments.

Background: Our textbook (Discovering Advanced Algebra) uses recursion to build into linear functions and exponential functions.  Our district decided at the beginning of the year that we could take the geometric recursive sequences and teach them at the intro to exponential functions.  The student teacher I’m working with had the idea that we could use credit cards to make a real-world connection.  Unfortunately he got saddled with all of the lesson planning for PreCalculus and never got to flesh out the idea.  So I hopped on that train and made it into a groupwork jigsaw activity.
What makes it a groupworthy task:  credit card calculations involve a lot of separate pieces of information, and you don’t need to be an expert on every aspect to grasp the whole, but you do need the basics.  By dividing up the resources of content knowledge, the final group has a reason to seek a contribution from each member.

Activate Prior Knowledge: We opened with the warm-up to make sure students were all clear on percentages, and finding increase and decrease.  In years past this was tricky, but it was smooth sailing this year.  The discussion questions at the end of the warm-up helped a ton to prepare them for presenting their work to the rest of the class.
Grouping: Each group of four students were assigned individual expert tasks.  They split to meet with their matching experts from other groups & work through their sheets.  The FEES experts have an actual credit card offer on the back of their sheet.

Products: After completing their requisite tasks, they head back to their original groups, and get the overall Task Card.  In a 100 minute period, this is where we had to stop and we’ll continue on Monday.

The final product will be a public vote tally on which credit card is “better.”  I haven’t figure out how to guide that into a mathematical argument.  Perhaps each vote needs to put up 2 reasons for the vote, and discussion will ensue?  I have to see it play out once and then decide what can be added.

 

 

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