“Your balance comes to $25.36, sir.”
You hand the clerk two twenty-dollar bills.
Quick — what is the change the clerk will give you? Can you get the answer before the clerk tells you?
If you buy a $23 item with 8% sales tax, can you come up with the exact final price in your head? Can you do it less than 20 seconds?
We live in a world saturated with calculating power. Your dishwasher alone probably has enough calculating power to displace millions (billions?) of humans doing arithmetic.
So what’s the point of mental math? Is it an obsolete skill?
Here are 3 good reasons you should work on your mental math skills. And I have a 2-Minute, 2-Week Habit Challenge to go with it.
Reason 1: It’s Practical
Sometimes calculators aren’t handy. Sure, you probably always have an electronic calculating device nearby (e.g. your smart phone). However, situations arise where it doesn’t always work to grab an electronic device.
I’m a chemist by profession. When I’m in the lab, my hands are gloved so I can handle hazardous chemicals. If I need to change a dilution factor on the fly, it’s very helpful to be able to do the calculation in my head.
You may not be in a science lab regularly, but you probably have similar situations come up. Maybe a recipe needs doubling while hands are covered in dough. Maybe you need to substract two length measurements while cutting boards for a project. Maybe you’re outside with winter gloves and need a quick estimate on a measurement.
Sometimes, hands-free calculations are just the easiest.
And sometimes, they are just faster.
If you can calculate change in your head, you’ll be able to get the answer far faster than the time it will take to pull your phone out of your purse or pocket, unlock it, open the calculator app and plug in the numbers. You’ll be surprised at how much more quickly you’ll get answers than other people who are fumbling around with their devices.
Reason 2: Keep Your Brain in Shape
I’m all for outsourcing mundane, repetitive tasks. It’s a key to productivity. Outsourcing mundane calculation activities to computers enables efficient, accurate, and reliable execution of number-crunching.
I would quit my job if I had to do all my work-related mathematical calculations without a computer. I would probably get fired for making too many mistakes, anyway.
So why bother with mental math?
Consider that we have cranes that can lift thousands of pounds, and vehicles that can travel at hundreds of miles per hour. Now consider how many people get gym memberships to lift 50-pound weights and sign up for marathons to travel 26 miles by foot.
Although cranes, planes, cars, trucks, and hydraulics could complete all of our exercise tasks with little effort, the point isn’t to simply complete the tasks. We need the physical exercise, or our bodies will atrophy.
Similarly, doing mental math can help keep your brain fit and nimble. You don’t need to be mathlete and join mental math competitions. However, a little work at mental math every day will keep your brain in shape.
The great part about mental math is that you don’t need any special equipment, programs, or software to practice. You can find the mental math equivalent of a gym almost everywhere you go. In fact, I’ll give you a free mental math ‘starter gym set’ in the link below.
Reason 3: Boost Your Confidence
Back to the weight-lifting comparison, I personally started lifting weights consistently only about a year or two ago. I was amazed at how quickly my muscle strength and capacity grew over time.
Now, I’m not a ‘muscle-guy’ by any stretch of the imagination (think skinny, medium-build, nerdy white guy). However, even with some limited, but consistent, weight-lifting workouts, I significantly increased my ability to lift heavy objects.
I found that as I gained muscle mass, not only did I feel good about an improving body image, but I also gained confidence in my new-found weight lifting abilities. Now, when I’m helping a buddy move furniture, it’s a great feeling to know I can help out without being — quite literally — the weakest link on the team.
Similarly having mental math skills will boost your mental confidence. It’s hard not to feel smart when you can calculate a 20% tip on a $39.50 dinner without using an electronic device.
And it’s hard not to feel good when you feel smart.
Build a Habit: 2 Minutes for 2 Weeks
How do you start on a mental math exercise routine?
Like all good habits, don’t start out too big. Start small, but be consistent. Use the pattern of BJ Fogg’s Tiny Habits:
1) Determine a prompt — when will you practice your mental math each day? Set a prompt that will remind you.
2) Make your habit a small, easy step. Keep it to 2 minutes of practice per day (at first).
3) Celebrate the completion of your habit. Smile, high five, sticker on a chart. It can be small and silly, but if it feels good, it will help lock in the habit.
4) As you consistently work on your habit, let it grow. Do a little more each day.
For some more detail on habits, read You Should Do 2 Pushups a Day for 2 Weeks. You can also find more extensive details on habit formations in BJ Fogg’s book Tiny Habits (highly recommended).
Take 2 minutes a day to do some mental math — addition, subtraction, multiplication, or division. Do this every day for two weeks.
You can devise your own math problems. Or if you’d like a jump start, sign up below, and I’ll share a free copy of 2-minute-a-day problem sets. In addition to some quick problems to do every day, it also contains some tips for helping you do mental math quickly. Consider it my gift a of a starter “mental math gym set.”
While 2 weeks will help you get started on this habit, don’t stop after 2 weeks. The goal is to start a habit of practicing mental math in an easy way. Like lifting weights, the more you do, the better you’ll get.
What are the results of this practice? Several years ago my wife and I started doing exercises every evening out of the 1945 book How to Calculate Quickly by Henry Sticker (also recommended if you want additional practice).
My wife is a self-described “non-math” person, but was a good sport in doing these exercises with me each night. Despite some initial reluctance, she found that after several weeks she was much more comfortable doing mental math. She would calculate change owed her at the store before the clerk would tell her the result. She felt the confidence of growing mental math muscles.
Even though we didn’t keep up the couple habit of doing mental math together (yes, you can imagine how this habit might die), my wife says that even for that short period, the extra practice helped her in a lasting way.
So don’t let your brain just sit there like a couch potato when an arithmetic problem comes along. Get it up and working for at least 2 minutes a day. You’ll see the difference!
Get Your Mental Math Gym Set
Sign up here and I’ll send you a free “Mental Math Gym Set” PDF to get you started. I’ll also keep you apprised of other 2-Minute, 2-Week Habits that can challenge you this year to improve your Body, Mind, Heart, and Spirit.
Now go forth and calculate!