Monday, December 1, 2014

Finding Perimeter & Area of Irregular Figures

I'll be honest, I HATE working on perimeter and area of irregular figures!  It is such a challenge for students and the perfectionist in me can't deal with the mess that these drawings quickly turn into.  This year, I did something extremely basic but so close to my heart; color coding!!!  I have found this method to be very effective for teaching students to visualize how to find the "missing" measurements.  It can also be done quickly, on the fly, and without ANY preparation.  


I begin this mini-lesson by telling students to grab two markers of their favorite color....talk about instant engagement!  I have them draw the irregular figure in pencil as I draw it on the Promethean Board.  Then I slowly have them color code the lines.  I usually begin with the horizontal lines only.  After color coding the horizontal lines, I ask the students to visualize what the shape would look like if we could somehow shove the "4 in" in the picture above down to be even with the "6 in".  I usually get responses like, "It will look like a rectangle..." and "Then it would be the same size as the 'unknown' purple piece at the bottom...".  All of which are *perfect* for solving the problem.  Using their responses, we begin discussing how to find the measurement of the unknown piece.  Then, we switch gears and do the vertical lines in another color.


I also like to give plenty of examples where students are given the long side and must use the colors to figure out one of the short pieces using the same process.  If you can teach your students THIS in a snap, then you deserve a serious reward!  

I also wanted to share a link to my Perimeter and Area Task Cards.  This packet of task cards includes ten sets of cards covering the following skills:
  *Finding Perimeter {with basic math facts and working towards double digits}
  *Finding Perimeter {with double digit numbers working towards triple digits}
  *Finding Area {with basic math facts and working towards double digits}
  *Finding Area {with double digit numbers working towards triple digits}
  *Finding Perimeter & Area {with basic math facts and working towards double digits}
  *Finding Perimeter & Area {with double digit numbers working towards triple digits}
  *Finding the Area of Triangles
  *Finding the Area of Parallelograms
  *Finding Missing Numbers in Irregular Figures
  *Finding Perimeter & Area of Irregular Figures

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