The 10% Benchmark

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Objective

SWBAT find the percent of a number using 10% as a benchmark

Big Idea

If you can find 10% of a number, you can easily find many other percents of that number.

Introduction

10 minutes

Before I begin with the essential question, I will want to make sure that all students can easily divide a number by 10 by shifting the decimal 1 place to the left.  While they should have already learned this shortcut, I know many will need a reminder.  I will cold call students here.  I'll present a number, call a name, and expect them to provide that number divided by 10.  I will go through the entire class.  I will scaffold the difficulty of the problems as necessary. Because this skill is so basic (it goes back well before 7th grade), I have an anchor chart posted in the room that all can see.  It shows how to divide a number by ten by moving the decimal.  I will refer to this poster often throughout the unit as needed.

I will then present the essential question:  How can you find the percent of a number using 10% as a benchmark?  I think this may be one of the most useful skills to know in the "real world".  I'll let students know this - when finding a discount, leaving a tip at a restaurant, etc.  This benchmark is vital.

A simple problem is presented with a bar model.  We will complete the bar model and answer the questions.  This is so that we can see that to find 10% of a number, you can simply divide that number by 10 (MP8).  I'll ask students to explain why this works.  They should feel free to point to the bar model above to help explain their answers.

Guided Problem Solving

15 minutes

Students now find quantities in a circle graph.  Some of my struggling readers will over look that the circle graph represents 400 new books.  It might be necessary to point this out or ask someone in the class to answer the question:  "How many books does the entire circle graph represent."

I am focusing on multiples of 10% for this lesson, but I could not resist including a question here or there with a multiple of 5%.  

GP2 and GP3 ask students to calculate a tip and discount respectively.  We will have a formal lesson on discounts later, but I didn't think it would hurt to include a problem here.  

Independent Problem Solving

20 minutes

The independent section again follows the same format as the guided section with only a few changes.  I have included a percent over 100%, but it is still a multiple of 10%!  Also the extension section has percents that are not multiples of 10%.  The 3 given questions should be answerable by all.  I will ask the more advanced students to see if they can determine the value of each category.

Exit Ticket

5 minutes

Before we begin the exit ticket we will summarize.  1) How can you find 10% of any number?  2) How can you use 10% to find any other multiple of 10%?

Students will then answer 5 questions.  The first 4 questions involve a multiple of 10%.  Therefore, a successful exit ticket would have these 4 problems answered correctly.  Hopefully students can reason their way through question 5.  Even if they are not quite sure how to find 5% they should be able to say that 10% of $500 = $50, therefore less than $50 was spent on invitations.