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Math at the Grocery Store

Today is all about “Food for Thought”.

Let’s do an experiment.

Pretend you are at the grocery store.

You have $9.50 in your wallet and you forgot your credit card. You want to buy a watermelon which costs $4.25 and a gallon of milk which costs $2.99. Will you have enough money?

There are lots of ways you might solve that problem in your head.

Maybe you looked at those prices and thought “2.99 is almost $3. So… $4 + $3 = $7. Then add in the quarter and you get $7.25. But take away the penny from the $2.00/$3.00 conversion, and my final total is $7.24.  So yes, I have enough money.”

But can you still go to Starbucks afterwards? How much money will you have left over?

Now you might be thinking “$9.50 – $7.24 = about $2.25. I can afford a cup of coffee, but not a mocha.”

What you just did was real life math.

I bet your accuracy was fantastic.

But now let’s do another experiment.

Pretend you are in middle school. You are crammed into one of those super uncomfortable chairs with the attached desks. The teacher is some old guy up front wearing a weird tie. There is a vague smell of tuna-melt wafting through the room from the cafeteria next door.

You are taking a really important test. NO MISTAKES ALLOWED! Here’s the problem:

950 – (425+299) = ?

a) 475

b) 226

c) 329

d) 225

Now what are you going to do?

If you are like most people my age or older, you might have reached for a paper and pencil. Probably you stacked those numbers up and started borrowing and carrying. It might even be possible that your accuracy went down.

It’s too bad you couldn’t unleash your inner math instinct.

One of my favorite books about math is called The Math Instinct: Why You’re a Mathematical Genius (Along with Lobsters, Birds, Cats, and Dogs) by Keith Devlin. In the final chapters of the book, Dr. Devlin shares research about this phenomenon of grocery store math vs. school math.

In real life people form their own strategies for solving problems and tend to be pretty accurate in their calculations. In school though, those same people can be hit-and-miss as they attempt to crank out traditional algorithms.

Maybe you are better at math than you thought.

Give yourself permission to let go of the notion that there is one right way to solve a problem.

Give your children permission to explore and discover strategies that make sense to them.

Then imagine the possibilities…

If you can already do grocery store math in your head with kick-awesome accuracy, what do you think might have happened to your own math ability if you had been encouraged to follow that type of problem solving as a young child? Would you be doing algebra in your head? Would calculus be fun?

When a teacher forces a child to do something over and over again that doesn’t make any sense to them, how is that helping?

In my ideal world, “Drill and Kill” would be illegal.

The real art in teaching math to children comes from asking them questions about their own thinking and then listening. “How would you do this? What makes sense to you?”

It’s really hard to do that in the classroom, especially if you are responsible for 30 kids.

But the next time you are at the grocery store with your own son or daughter, try asking them if you have enough money to buy ice cream. Then listen to what they have to say…

Math Boot Camp for Moms, Day 2


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