Simple Interest

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SWBAT solve for simple interest on dollar amounts for example loans and deposits.

Big Idea

It is important for students to understand when borrowing money, they will not pay back only what they borrowed, but also an extra amount added on called interest.

Teacher Guided Notes

This lesson is intended to teach students how to calculate simple interest.  A more important emphasis with this lesson is to focus on what simple interest is.  To make it plain for students to understand, I explain that it is an amount that is accrued over a certain amount of time.  Simple interest can be an amount owed by a borrower, or an amount gained to be paid to a borrower.  To connect this to a real life experience that students will go through is Student Loans.  Common Core has a high focus on students being prepared for college and the work force.  As an opening example I use my own experience with paying back student loan amounts.  We are able to discuss vocabulary terms such as principle, rate, annually, interest, etc.  Please be sure students have a strong understanding of these terms.  When students are answering real world word problems a strong understanding of content vocabulary will be needed to calculate correctly.  Remember, the calculations are easy, coming up with the process to complete the calculations is the hard part. 

Unpacking the question is going to be important.  This strategy will help students scaffold the problem down through questioning which will lead them toward creating the correct calculations to solve the problem correctly.  Students will have a bell ringer, and a student activity.  The bell ringer includes scaffold questions, and the student activity has a teacher breakdown resource that will be helpful to use during the whole group discussion.  

Bell Ringer

15 minutes

Hand the students the Simple Interest Bell Ringer as they enter the door.  Students are to sit in the Individual Think Time seats.

You may want to do a quick vocal review of what students were able to accomplish thus far with this unit.  Students should use prior knowledge to work through the bell ringer.  Students should be able to see the connections between each lesson.  Students will work as individuals through the bell ringer for 10 minutes. 

After students answer each question in the bell ringer, allow them time to discuss their work with a peer or a peer group.  Afford students 10 minutes to have the mathematical discussions. This again is a great time for students to practice MP 3. Students will check their work, correct mistakes, ask questions, and discuss personal strategies used to solve the problem.  In the bell ringer, students are given two strategies to use to help find the dollar amount of the percent of increase.  They will be able to use proportional reasoning, or an equation.  It will be important for students to know they are not limited to these strategies.  They may want to use modeling as a strategy which is perfectly ok. (MP 4)

Student Activity

15 minutes

Once students have gone through their mathematical discussions, place them back into I.T.T time. Hand out the student activity.  You may allow your students to use their bell ringer to help them solve the student activity word problem. Students should work through the problem using (MP 1, 2, and possibly 4.)  The bell ringer is a modeled problem that scaffolds down a similar task.  This will help students understand what to identify within the word problem, and the questions to ask to solve the problem.  Allow students 5 minutes to solve the problem.  Have students discuss their work with a peer.  Students will check for understanding and accuracy.  (MP 3, and 6) Allow students 5 minutes to discuss.  

Whole Group Discussion

15 minutes

During this point in the lesson students are encouraged to share their mathematical discussions, discuss mistakes that were made, how mistakes were corrected, misconceptions, and final answers.  This is the time in which direct instruction can take place.  During this time, go through the bell ringer, be sure to give correct answers for each of the scaffold questions. This may be done through validation of student responses, or you going through each question and having the students check for correct responses.  Be sure to go through the thinking process of each.  Once you have the correct responses for each of these, go through the student activity word problem. Use the teacher resource guide to help guide direct instruction.  This guide breaks the problem down step by step.  


5 minutes

Reiterate that being able to answer a multi-step word problem will take using the prior knowledge gained from previous lessons.  This is the importance of consistent review of what has been previously taught.  Students need to see the connections from one objective to the next.  I have found, breaking a problem down into steps will allow students to make connections.