Math is Real Life - Grocery Shopping Edition - MATH NINJA, LLC

The grocery store is full of useful mathematics! Today’s post is about calculating unit rates to find the best bargain (Real Life Math!).

What is a unit rate and why is it helpful?
A unit rate provides you the cost of an item per one unit (ounces, pounds, feet, etc.). It is extremely helpful when comparison shopping and trying to save a little money. In today’s post we will use unit rates to compare the cost of cereals and corn.

On a recent visit to the grocery store I was shopping for cereal. I wanted to know if buying larger quantities of Raisin Bran Crunch would be cheaper. Lucky for me, Publix grocery store provides a unit rate along with the price of the item on the shelf. Take a look for yourself.

$Calculate the unit price for Raisin Bran Crunch at Publix$

I don’t have to wonder if $4.99 is a good deal for more cereal. I know it is the better deal because I can compare the unit prices. I would rather pay 20 cents per oz than 23 cents per oz. Even though the larger box appears to cost more ($4.99 vs. $4.19), in reality I am saving approximately 3 cents per oz.

Now, I don’t know about you, but I love shopping at Target. I am lucky if I can leave the store with a receipt under $100. My only complaint is they don’t provide unit costs! Check out the prices on Fruit Loops at Target.

$Calculate the unit price for Fruit Loops Target$

Thank goodness I have a calculator on my phone because I need to calculate the unit price myself. By dividing the price by the number of ounces, I am able to calculate the unit cost for each box.

$Screen Shot 2014-02-27 at 8.22.34 PM$

Based on the above calculation, the value size appears to be approximately 18 cents per oz.
$calculate unit rate 1$

Based on the above calculation, the box with a temporary price cut appears to be approximately 23 cents per oz.

It looks like the larger quantity is definitely the better buy. If I buy the larger quantity, I will save 5 cents per oz.

Now you may begin thinking that larger quantities always cost less per oz. Typically this is true, but not always. Let’s take a look at canned corn.

$Calculate the unit price of canned corn$

In the canned corn example above, the 29 oz can is actually the most expensive per oz. I will definitely be buying one and getting one free!

Does your grocery store provide the unit price, or do you have to do the math yourself? I’d love to hear about your experiences in the comments below.

Are you looking for other ideas about using math at the grocery store? Take a few seconds to read the post 10 Ideas for Using Math at Home. This post will provide you additional ideas of how math is used at the grocery store.

A monthly REAL WORLD math blog link-up hosted by
4mulaFun, Fourth Grade Studio, Teaching to Inspire in 5th, AND MissMathDork.

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$Angela Culley$

Angela Culley

Owner & Tutor at Math Ninja, LLC

As the founder of Math Ninja, Angela provides online and in person math tutoring for all ages including those studying for the GRE, GMAT, SAT, ACT, PPST, and other math specific subject assessments. Prior to launching her business, Angela coached K-12 educators on effective teaching strategies, curriculum writing, and assessment development.As a classroom teacher, she taught math to students ranging from grade 5 - 12. She has also taught both undergraduate and graduate math courses as an adjunct professor at the University of Virginia and Mountain State University.

$Angela Culley$

Math is Real Life – Grocery Shopping Edition

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