7th Grade Math : Unit #6 - Geometry : Lesson #11

Circumference from Area / Area from Circumference

Objective: SWBAT determine the circumference of a circle given its area and vice versa
Standards: 7.G.B.4 MP1 MP3 MP6
Subject(s): Math
60 minutes
1 Teacher Model - 10 minutes
Suggested Changes
Adjustments to Practice

In the reflection from the previous lesson I suggested setting up the lesson so that students discover how to find the radius and diameter when given the circumference or area of a circle.  Using that approach allowed me to skip most of that lesson and combine it with this lesson.  This saved me a day in my unit which I could use later for re-teaching or extending a concept!  

I started this warmup with a short refresh on finding the radius and diameter.  I then allowed students to try the examples on their own.  I only had to help a few students find the radius and diameter.  Most then saw that once they find the radius from a given circumference they can then use that radius to find the area.

2 Guided Practice - 10 minutes

The students will work through the guided practice problems using their notes and partners as a resource.  These problems mirror the example problems, but also  include problems where 3.14 is used for PI.  I will monitor student work looking for common problems to bring to the attention to the entire class. 

3 Independent Practice - 20 minutes

Students now work independently on the next set of problems.  These mirror the work just done, so students who are having difficulty should have several models to refer to.  If I am asked a question, I will first point students to those models from the examples or guided practice. 


The extension problem is included to provide another “real-world” area and circumference task.  Part I requires students to explain their thinking (MP3) .  It requires an attention to precision (MP6) as students must realize that the radius is not the same at all points on the walkway.


4 Exit Ticket - 5 minutes

Students take an exit ticket.  The first two problems are multiple choice to catch common errors through the distracter items.  Problems 3 and 4 are open ended.