Working With Percentages to Estimate & Calculate Discounts

The following lesson resource material provides Real World Math Problems that were created with the Grade 6 Ontario Mathematics Curriculum in mind. 

Teachers from Ontario schools as well as schools world-wide are welcome to use this lesson and series of videos/photos in their classroom to engage their students with a real world application to strengthen the estimation and calculation skills of percentages as well as apply their understanding of discounts as a percentage. Throughout the lesson, students are asked to estimate the cost of each item of clothing after a discount is applied while encouraging the use of friendly numbers and their understanding of percentage as a part (percentage) of a whole (out of 100). Students will then be able to take their estimate and complete the calculation with a calculator to compare their estimate with the actual result.

Learning Goals:

After our Real World Percentages Math Lesson, I will be able to:

• estimate quantities using benchmarks of 10%, 25%, 50%, 75%, and 100%;
• calculate percentage quantities; and,
• apply percentage discounts to find the sale price of an item.

Act 1 – Introducing the Task

Show students the act 1 video.

Then, ask the students:

What do you notice? What do you wonder?

Give students some time to jot down some of their noticings and wonderings on a piece of paper or on a whiteboard/their desk with non-permanent marker. I generally give a minute of time for students to do a “rapid write” of these ideas.

Then, I have students share out their noticings and wonderings while I typically list them in point form on the whiteboard or in a note on my computer on display for all to see. Attaching names to these ideas can be a nice way to build in some accountability and encourage sharing.

Since the price is clearly blocked out in the video, I hope someone is curious about the price and or discount price of the suit jacket with some ideas like these:

How much does it cost before the discount?
How much will the discount save you?
What will be the sale price you have to pay?
And many more…

While the questions I’m fishing for don’t always come out, that is O.K. The discussion is key in order to hook in my students and their curiosity can be moulded quite easily after they have shared out so many interesting ideas. We often spend some time trying to answer their other curiosities in order to ensure students know that their voice is valued.

Then, I ask students to make a prediction.

I’ll have students share out these predictions, jot down their names and try to get a bit of friendly competition going on in the classroom to bring about student discourse in our non-threatening classroom environment.

Act 2 – Give Some Information

We will then have students watch the act 2, scene 1 video to reveal the original retail price.

The teacher can then ask students to have a discussion in their table groups to determine ways that they can go about estimating the sale price after the discount. Some guiding questions:

• What are some friendly percentages we can use to help us get a close approximation?
• Does rounding the retail price to a friendly number help here?
• and so on…

After the discussion, students can share out via Apple TV or using chart paper in your classroom to model as many creative solutions as possible. Students can then check their estimates using a calculator and possibly encourage them to try and find a more efficient strategy as they move through the remainder of the tasks.

Act 2, Scene 2

Students will watch the act 2, scene 2 video.

Students can then use estimation strategies to find the discount and the sale price of the item.

Act 2, Scene 3

Students will watch the act 2, scene 3 video.

Students can then use estimation strategies to find the discount and the sale price of the item.

Act 2, Scene 4

Students will watch the act 2, scene 4 video.

Students can then use estimation strategies to find the discount and the sale price of the item.

Act 2, Scene 5

Now, students are asked to calculate a sub-total and determine the total bill we should expect when purchasing all four items.

Act 3 – Show The Bill

Then, you can show what the bill would look like for students to confirm their thinking. Since I live in Ontario, I’ve shown a bill here using the Harmonized Sales Tax (HST) of 13%:

Something else I typically do with my students is have them figure out how much the bill would be in Michigan, since we are so close to the border and many families go across to Detroit and the surrounding area to shop:

Here’s an image with the final bill from Birch Run, Michigan:

Additional Discount Photos For Classroom Use:

Suitable for the Following Ontario Mathematics Curriculum Courses:

• Grade 6 Mathematics
• Grade 7 Mathematics
• Grade 8 Mathematics
• Grade 9 Mathematics
• MAT1L – Locally Developed Mathematics, 9
• MFM1P – Foundations of Mathematics, 9
• MPM1D – Principles of Mathematics, 9