## Thursday, May 21, 2015

### Rugs Re-Engagement: Perimeter, triangles, and circles

I gave my 8th grade students this task to work on for the last 15 minutes of a class period. I told them that we would revisit it. And they'd get a chance to revise it and finish it after a lesson.

All of the resources are available at http://www.insidemathematics.org/assets/common-core-math-tasks/rugs.pdf for free. It definitely hits on lots of topics.

I feel that the most common mistake was English standard system measurements being converted to decimals incorrectly by my students. This had come up in the Dan Meyer Taco Cart 3 Act lesson that we had previously done.

GOALS:
1. Address a common mistake as a class and analyze it.
2. Give reason for your own mistake after analyzing it and write it down.
3. Cross out your incorrect answer, and correct it with work shown.
4. Turn in for a final grade.

So, let's analyze the first most common mistaken answer for #1: students getting an answer of 13.2.

• What mistake are they making?
• How can you show your work using a formula?

In the next problem, for the perimeter of the triangle, the most common mistake was getting an answer of 7. There were A LOT of people that had no response also.

• What are students incorrectly assuming?
• How does the fact of knowing what an isosceles triangle help you in this problem?
• What does perpendicular mean? What does perpendicular height mean?

In the third problem, a lot of students made the mistake of not following the directions of giving their answer in whole feet. The main wrong answer we will analyze is the answer of 31.4.
• What are the students incorrectly assuming?
• What do they need to know about parts of circles to not make this mistake?

In the final problem, most students either did not give a response. The most common mistake was 7.85.
• What are students not accounting for if they gave that answer?