Multi-Step Percent Problems
Today, my colleagues and I decided to do a flexible grouping activity in 7th grade: We gave students a pre-test on their understanding of percents, and created three different activities based on their pre-test scores. We differentiate in readiness groups: Support group, Target group, and Enrichment group. This week, I took the enrichment group and brought my colleagues on board with my doing a computer programming activity. I was extremely nervous about this. My students have been coding since fairly early in the school year, but this would be a first introduction for kids from other classes. I did not know whether I could make the learning target engaging in a coding format and accessible to everyone. Here is the learning target:
I can use proportional reasoning to solve multi-step percent problems.
Common Core: 7.RP.3 Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.
Yes, we did just re-state the standard and make it a learning target!
For reference, these documents are the Support and Target activities. They were terrific problem-sets, interesting, accessible, and engaging.
I thought and thought about a good application of the standard, and I really wanted to make it visual so the students could get instant feedback on whether they were on the right track. I decided an area application would be a good rigorous activity, and it would also include elements of:
7.RP.1 Compute unit rates associated with ratios of fractions, including ratios of lengths, areas and other quantities measured in like or different units.
Thus I created the Sod activity. This is a “Wreck-it Ralph” problem. The premise is that I tell the kids I used to have a working computer program, but Wreck-it Ralph got into my program and broke it, and they have to fix it. They get very excited about Wreck-it Ralph.
I randomly assigned kids to groups of 2 or 3. I gave each group a worksheet as a space to show thinking and organize their discussion. Every group had to have one scribe / communication leader, and one “runner” whose job it was to ask other groups for help if they got stuck. I read the situation and we talked about what sod was, how it was sold in rolls that unrolled into rectangles, and how it was priced. I showed them the computer program and the structure of the 3 problems inside – each problem had a rectangle and a pricing problem to solve.
Kids really dove in very quickly and started tackling the problems. I got summoned over to help a couple of groups start, but groups that did not see me right away still attacked it. Some groups were having better discussion than others, but all groups were discussing the problems. They wanted to show me their computers and ask “is this right? Is it?” I answer questions with questions and they know this by now. “Why do you think it’s right? Does the sod cost $3.50 per square foot? Are you sure that is 10% bigger? Why did you divide there?”
Not all groups finished every problem, and there are still misconceptions that need worked out. This is part of why we do this, though: to identify, diagnose, and plan for how to expose and break down the misconceptions later. Some interesting discussion items that came out of the activity:
– Identifying the unit price as $3.50 per square foot instead of $0.35 per square foot.
– Assessing reasonableness of answers (should sodding a yard cost more than a Land Rover?)
– Calculating tax only instead of price + tax
– Using 0.43 as the tax rate instead of 0.043
– Different strategies to increase by 10%: w + w*0.10, or 1.10 * w for example
– Increasing length AND width by 10% instead of only increasing one dimension by 10%. Discussing which strategy actually increases area by 10%
– Identifying that 20% off is the same as 80% of the original price (price – price*20 is the same expression as price*0.80)
– Deciding whether a 10% increase followed by a 20% decrease is the same as a 10% decrease. This created a fantastic discussion at the end of one class.
I selected a couple of kids to share their solutions to problems #2 and #3, and invited others to have discussion on the solutions using appropriate sentence starters. We did not summarize all problems. Kids said their “brains hurt”. I asked them to write two of their biggest “ah-ha’s” on a sheet of paper and turn it in. I don’t know why I used treeware at this point. I do like the tactile experience of shuffling through paper, but I probably should have had them turn reflections in on a Google form.
Reflections: Some of the more interesting samples from kids. I wish I had given them a better prompt. I did not get very mathematical reflections from most of them.
This was a phenomenal modeling activity. Really. There are more ways to slice this problem than even I realized. The kids loved it more than I thought they would, even though I cautioned them we would be doing math about grass all period.
One unexpected benefit was that students also created different equivalent expressions, aligning their lesson with:
7.EE.2 Understand that rewriting an expression in different forms in a problem context can shed light on the problem and how the quantities in it are related. For example, a + 0.05a = 1.05a means that “increase by 5%” is the same as “multiply by 1.05.”
What are the other benefits, and risks, of an activity like this? What math skills did they gain? What are pitfalls I didn’t notice?
I leave you with a picture of happy kids coding.