Performing with Percents - Can you bust some common misconceptions?

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Students will be able to develop a mathematical explanation disproving some common myths regarding percent.

Big Idea

Do a 20% increase followed by a 20% decrease cancel one another out? Students will develop their own mathematical examples and written explanation to bust some common myths.


10 minutes

OpenerThe opener for this lesson is a little different than my normal opener.  Today I am focusing on getting students to think outside of the box, and reason with one another - which ties in mathematical practice 3 and mathematical practice 1.  For today's opener, students will be given a 10 x 8 grid and asked to show a visual of what 15%, 0.725, and 3/16 would look like on that grid - without using a calculator or doing out any calculations. Instructional Strategy - Process for openers

Learning Target: After completion of the opener, I will address the day's learning target - "I can apply my knowledge about percent to clear up common misconceptions."  Students will write this target down in their student planners.


45 minutes

Percent Applications Performance TaskIn a recent observation, my administrator could not wrap her brain around the fact that taking a 9% discount on a number, or placing a 9% increase on the answer would not give you the same result.  In fact, I had a student go to the board and work out the problem "after a 9% discount, an item is $91, what is the original price of the item," and the administrator in the room could not figure out why you wouldn't just increase $91 by 9% - she disagreed with the fact that you would in fact have to use division to figure out this problem.  If a person in her position had that misconception, it led me to believe that many people probably have that same misconception.  Therefore, today in class my students are going to bust some common misconceptions!  In their table groups, students are going to be given one common misconception or problem to work with.  Their job will be to answer the question posed, and then to each develop a mathematical example that supports their answer, and come together to write one short narrative that describes the mathematics behind their answer (a generalization of why it will always work, regardless of the numbers).  This task is a good use of mathematical practices 3, 7, and 8, as students will be reasoning together and using what they already know to write a generalization about a certain concept. 


5 minutes