Discounts and Sales Tax

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SWBAT solve discount and tax problems using benchmark percents

Big Idea

Can you buy a $5 Footlong for five dollars? How much will an item cost after a 20% discount?


10 minutes

I'll begin the lesson with the essential questions:  How can you find discounts and sale prices?  How can you find sales tax and totals?  This is to make sure students are aware of what should be accomplished during the lesson.  

Students often have difficulty distinguishing between discounts, sales price, and savings.  So I will ask what does it mean for an item to be on sale?  What is a discount?  What is a sale price?  What is a savings?  How are these represented?  This is meant to be a quick discussion so if students are unable to come with a relevant answer, I will provide the correct answer.

I'll then ask:  Can you go to Subway with only five dollars and leave with a five dollar Footlong?  Students will not the answer here is no.  Most will know the extra is tax.  I always like to add the anecdote that sales taxes vary from place to place.  For example, the sales tax in neighboring Jefferson Parish is different than sales tax in Orleans Parish.

Also to help with vocabulary, I have included a graphic organizer.  This would be a good anchor chart to have posted in the room also.

Next we cover vocabulary.  I will have students draw an arrow to the box that says discount amount and label the arrow "Percent of Original Price".  The box should also be labeled "Savings".  Students will draw an arrow to the tax amount box by writing "Percent of Item Cost".

Next I will  model two examples.   Students will be expected to model work in a similar fashion.

Guided Problem Solving

15 minutes

Students will now work on 3 guided practice problems.  They will be encouraged to check their notes and use neighbors as a resource before asking me.  If I notice students are struggling to make sense of the terms savings, sale price, sales tax, etc.   I will make a show of taking a look at the notes as a way of help.  I might point to it and say "Oh... the sale price is the original price minus the discount".

The first two problems are similar to the previous examples.  The  third problems is just a bit more complicated; it involves a discount and adding sales tax.  It may be necessary to tell students that sales tax is based on the sale price or discounted amount and not the original price.  Look out for students that overlook "3 games". They may accidentally find a total on $40 worth of games versus $120 worth of games.  

Independent Problem Solving

20 minutes

Students now work on their own to solve the next 8 problems.  If time is short, I will want to make sure they finish the first 5 problems.  Problems 3 and 4 require students to round to the nearest cent.  I know this will be problematic for more than a few of my students - yes, even in 7th grade.  I'll take it as as opportunity to reteach rounding!

I love problem 6 because part C tries to bring out a misconception.  Some students may think that a 30% discount with an additional 20% off the sale price is equal to a 50% discount.  Careful readers will indeed note that it is an additional 20% off the sale price. 

Problems 7 and 8 are meant to build off the work we've done with bar models to find equivalent expressions.

Exit Ticket

5 minutes

Before beginning the exit ticket, we will review discounts and sales tax.  It might be as simple as how do I find a discount or sales tax?  How do I find a total including sales tax?  How do I find a sale price if I know the discount?

I like multiple choice exit tickets from time to time.  Especially as we get closer to test season.  I will still require that my students show work and annotate what they read.  This will hopefully help them avoid falling for the distractor answer choices.

Question 5 is open response.  It requires finding a total after applying a discount and sales tax.

Students should be able to score at least 4 out of 5 on this exit ticket to show mastery of the lesson.