Simple and Compound interest: a sorting activity

This is very basic, and does several good things:

• Connect to student understanding of sequences and series (which we had studied the previous weeks), percent, and functions (mine haven't studied exponential growth yet).
• Get students discussing concepts such as interest rates, loans and repayments
• All my students were very actively engaged with thinking and arguing about this activity
• Somewhat self-checking, especially once I told the kiddos that the two columns should be of equal length

What to do: 

1. Cut out each rectangle and give small groups of students a set of all the rectangles. 
2. Tell them to sort them into two categories. Or don't tell them the number of categories. 
3. Eventually hint that the categories should have equal number of rectangles.
4. When groups are almost done, walk around and check on their categories, giving hints and pointing out conflicts without giving the solution to the conflict.

When groups are done, I lead a whole class discussion in which the main ideas of simple and compound interest were introduced and defined, and students got a few minutes to derive the general formulas for these types of interests. 

I ended the lesson by asking how much Jesus would have had in the bank today, if his parents had invested 1kr at 1% annual interest when he was born. This helped students get the idea that given enough time, compound interest far outgrows simple interest.