Sep 22, Mental Math at the Register

coins mental math

To stay sharp, look for ways to exercise your brain in daily life. Mental math while you are out-and-about is a great example.

Solving math problems in your head trains quantitative intelligence (Gq). It also requires focused attention.

I play a math coin game at the store sometimes when paying for small purchases. I'll carry an assortment of small coins in my pocket for this purpose.

One such game: "Receive multiples of 25 cents in change."

Recently I bought an Americano at my local coffee shop. That's my favorite coffee drink. Splash of heavy cream and two Stevias. Total owed $2.98.

Time to pay. Not with three one dollar bills. I'd be burdened with two more pennies, and not train my brain.

Instead a mental math challenge!

I prefer the "counting down" method. It's the opposite of the counting-up method used by cashiers to make change.

Here's the thought process. Multiples of 25 cents are zero, 25, 50, and 75. For the coffee I owe 98 cents. The next-lowest multiple of 25 is therefore 75 cents.

I count down from 98, starting with pennies. Dropping from 98 to 95 is three pennies. Now I have options. I can drop 95 to 75 with two dimes or four nickels or two nickels and a dime.

I get out three one dollar bills and hand the cashier $3.23. The cash register checks my math: $3.23 - $2.98 = $0.25. I'm handed a quarter. Victory!

I'm glad to get rid of the small coins of little value, especially the pennies. It’s a good way to use up the small change I've thrown into a drawer.

Is this game trivial? No. All mental challenges are beneficial. Even small ones.

They force you to pay attention, to concentrate, to focus. And in this case, to calculate.

Consider the alternative: To passively not use your brain, as when swiping a credit card or handing over three one-dollar bills. Even a little counting-down game is a plus.

If you need practice counting coins, play the free Cash Back money counting game here on my site.

During the course of your day, look around for opportunities to challenge your brain. Be creative and have fun. Stay sharp!