Jana Henry's (Dixon High) Reflections About This Activity

Car Lab

This lab was really fun and the kids enjoyed it.  We brought in laptops, which worked well in the classroom.  The lab can also be done in a computer lab if laptops are not accessible.  The kids liked the fact that they were able to choose the cars they wanted to research.  It gave them ownership of the math they were discovering.  What was also very interesting was that each group had different situations occurring with the two cars they choose, which is impossible with a predictable table given to them in a textbook.  Some groups had more expensive cars that were losing value faster than the cheaper car, others had the more expensive car with a better depreciation rate, and some groups had missing years, which brought up the problem of having to estimate the value of the cars during those years.   We were able to talk about the power of the multiplier and how it affects the value of the car.  We talked about why a car would lose its value quickly or why it would hold its value better than others.  We also talked about the intersection point of the two models and how they would be able to tell if they would ever be the same value. 

One thing to watch for is the car that they choose.  Make sure to tell them that they need to choose a car whose value goes down over 5 years and never increases in value.  If they used that particular car, their data would not be exponential.

Another thing to keep track of is when they finish collecting the data.  With the laptops I only had to look after 8 computers but as they finished I noticed that I needed to turn the computers off.  They have a tendency to want to watch the videos of their cars and so on.  It wasn’t a big problem; it was just something that I knew I had to regulate. 

One important thing about this activity is to keep the groups thinking about the mathematics of a depreciating car.  For the faster groups ask them why the cars would be depreciating at the rate they found.  Have them make predictions about the value of their cars in different years and what might make their prediction a good one or a bad one, from the models that they found.  Also, ask them questions about the intersection of the two models and why they would or wouldn’t intersect.  For the groups that get weird data talk about why it would be unusual.  And for those who are a little slower give them help when needed. 

Several discussions can come from this lab. One can be the reason for taking the average of the percentages over the years.  Also talk about why the data looks linear, since it is only over 5 years, but why they are finding exponential models.  Either way it is important to point out all the levels of mathematics in this activity if the subject arises or if you find it necessary.