Marketing Percent Blunder

Personal Reflection:
As I stated in my previous post, I'm seeking relevant, engaging percent problems for my students.  Earlier this summer I received an email advertisement from a company that I frequent.  (Who doesn't love amazing balsamic vinegars and olive oils??)  However, my "mathematician brain" quickly targeted the 60% off claim.  I was so disappointed that my $21 bottle of olive oil was STILL $13.  Something smells fishy.  :)  I think my kids should talk about this one!

Grade Level: 6-8

Course: Math, Pre-algebra

Standards:   7.RP.3

SMP: MP1, MP2, MP3, MP6
Skills:  Solving problems with percents, finding percent increase, analyzing and interpreting mathematics.

How to use this as a mad minute:
There are a variety of questions I'd ask students to consider for 60 seconds or less:

• What is the difference between paying 60% of an item's cost and a 60% discount?
• Which of those would you use if advertising a 60% savings?
• Can you estimate the cost if you were saving 60% on the advertised bottle of olive oil?  (Note:  I use estimate because I want students to round the price and use mental math, not calculators on such an estimate!)

How to use this as a warm up:
This question feels a bit more like a warm up than a sprint.  A few more minutes to consider the phrasing, the numbers, and the claims.  If your students are proficient or nearing proficiency with the skill of percent discounts, they should be able to attack this independently.  I'd simply ask, "Do you agree with this ad?  Why or why not?"

How to use this as a mini-lesson?
I like the "Mini-lesson" feel of this ad more than anything.  I know that we'd need more than 5 minutes for this conversation, but not nearly an entire class period.  We use Connected Math at my school and this feels like a great "Launch" into other explorations of discounts.  Some questions I'd ask in a mini lesson:

• Use the warm up questions.
• Using the two prices provided, find out what percent you PAY of the original.
• Using the two prices, find the percent DISCOUNT off the original.
• What do you think of the claims made here?
• What math might the owners of this business have done to get to their conclusion?
• Can you create a more accurate ad for this business to use?

ALSO, if you have technology readily available in your classroom, I would use it to have the students "draft a response" to this advertisement email.  This will increase their literacy skills, their communication skills, and their skills at justifying their mathematical thinking.  Plus, it's a great civics lesson to work with community members to keep informed.

How to use this as a full lesson?
If this were your students' first introduction to percents, percent change, and discounts, I can see how the exploration of these relationships using this problem might last a whole hour.  My advice for such a lesson is to really scaffold the instruction and questions to help guide students to the realization that this may not be accurate.  Of course, this depends on the culture of your classroom, the instructional strategies you use, etc.

A quick outline of what I might try:

• Show the ad, explain that "mathematicians wonder mathematically" and we might wonder if this is accurate.  We are going to build our skills so that we can analyze this ad successfully.
• Start with the meaning of percent, how to find a percent given two numbers.  Do some samples.  3/5 is 60%, 2/8 is 25%, etc.  Talk about the meaning of those percents.
• When they see an ad that says 25% off, what does that mean?
• What does "off" mean mathematically?
• If we know how to find 25% of a number, how do we find 25% OFF of a number?
• If we are taking 25% OFF, what % are we paying?
• What's another way to find the cost?  (Find 75% OF the number instead of 25% OFF)
• What's the difference between PAYING 60% and SAVING 60%?
• Show the ad again, and ask them to figure out if the ad is accurate.

How to use this as an assessment?
If your students are ready for an assessment, they are ready for this.  Simply ask them if the ad is accurate and why!  :)


Please feel free to use any of these ideas and modify them to meet your needs.  However, please acknowledge the original source of the items and my own lesson outlines.  ©NatalieRSprigg 2014