This article was published in the 17-Apr-2014 issue of Finweek Magazine

Do you hit a mental wall when calculating numbers in your head? You’re not alone. Mental maths doesn’t come easy to everyone and most people find it challenging to master. Why is it important and how can you hone this critical skill?

When faced with a tricky maths calculation, how many times do you whip out a calculator or have Excel solve it? Virtually all of us do. This may be easy, but you’re not honing your mental abilities. But so what? The question that many people ask is this: why do we need to do mental maths when we’re out of school and have computers and calculators to do the work for us? What’s the benefit of mental maths?

Mental calculation sharpens your brain and boosts mental agility, concentration and memory. Research show that keeping the mind active helps to protect it as we age. A recent study revealed that regular brain-stimulating activities helped to prevent dementia and Alzheimer’s disease.

Mental maths, memory training games, and brain games like Lumosity are just a few ways to keep your brain sharp and active. Not surprisingly, the “brain fitness” wave is a budding new space which some market research organisations estimate will be worth $4-8 billion worldwide by the year 2020. Although South African figures are hard to come by, a 2011 article in Business Insider valued the US brain games industry at over $300 million per annum.  Those are big numbers even if you don’t use mental maths!

Mental maths could also provide the added benefit of learning something new. Learning to deal with new situations stimulates your brain to create new neural messaging pathways that didn’t exist before. This process builds brain health in much the same way that cardiovascular exercise boosts your heart’s health. So if you haven’t used your mental maths since high school, just the act of reviving this long-dead skill could help get your brain into good shape.

In the competitive management consulting space, mental math is a vital part of the consulting recruiting process, according to Consulting Fact. You’ll need it at the case interviews and probably also in the tests that consulting companies pose for candidates (take the McKinsey Problem Solving Test for example). And you can’t always depend on a calculator – especially if you need to pass job-interview or business school exams like the GMAT, with lots of math problems.

Here are some practical suggestions you can use every day to sharpen your mental math skills:

1. Work out the total in your head
Whenever you buy something, try to calculate the total cost of your shopping “basket”. This improves your adding and multiplication skills. Start with small spends like buying petrol or movies for the family with popcorn and drinks. Battling to remember exact amounts?  Simply estimate the value you think your total will fall above or below. For example, let’s say you’re filling up with petrol, and your petrol tank takes 60 Litres at R14.50 per Litre for 95 Unleaded. Rounding up to R15/L, you can calculate your rough total as R15 x 6 i.e. R90, and multiplying this by 10 equals R900. So you know the wallet damage will be less than R900.

As your mental maths gets better, stretch yourself by doing more accurate approximations, and estimate the total spend of bigger shopping trips like the dreaded monthly grocery shop. Cross-check the accuracy of your estimate against the shop receipt.

Where could this be useful in real life? Let’s say you run into the petrol station 24-hour shop to buy drinks and a loaf of bread on Sunday night, and you’re paying cash. What if the cashier either accidentally short-changes you?  If you cannot or don’t do your mental maths, you won’t even realise the mistake.

2. Check the per-unit cost
When you buy something that comes in different sizes, a tip from Consulting Fact is to compare the price per unit. Not only will this help you assess which size offers better value, it will also sharpen your division abilities. Interestingly, you’ll also find that many of the common assumptions don’t hold true, for example, buying in bulk is not always cheaper per unit. If the shops displays per-unit costs on their product signs, crosscheck these against your mental calculations.

3. Discounting
If you’re in a meeting with a client and negotiating around price, mental maths comes in handy when there isn’t a calculator around. Let’s say the client is keen to buy but wants a discount. So if your company sells corporate gifts, their question could go something like this: “If we buy 100 end-of-year gift packs at R100 each, what discount will you give us?” If you buy the packs wholesale at R50 each and add on a 100% margin, they are costing you R5,000 and you’re selling them for R10,000. Adding on overheads, packaging, staff costs, etc., the per-unit cost is R60. So you have R40 per gift pack to play with. If you gave the client a 20% discount on the R100 per gift, the R80 price per gift pack still leaves you with R20 profit on each, still a 25% profit margin. So you could safely  offer your client a 10% discount on 100 gift packs, going up to 20% on 200 gift packs. All of this mental maths helps you know how much room you have to play with when negotiating with your client.

4. Watch the time
Every meeting or event that runs for a set amount of time is a fantastic opportunity to sharpen your mental maths. During that boring meeting, work out the percentage of time that’s passed. Somehow knowing that it is 60% over, makes it less painful! Or what about swimming 1600m when training for the Midmar mile? The 1600m amounts to 64 laps in a 25m pool. If you’ve done 48 laps, you’re ¾ of the way there, which is a big motivator to keep going.

On the lighter side, if like me, you can’t stand meetings just for the sake of meetings, the “Meeting Ticker” is a fun tool to measure how much money is spent attending meetings. Go to http://tobytripp.github.com/meeting-ticker/, enter the number of attendees, average hourly salary estimate, and meeting start time, and watch the dollars add up in real time (If you want to practice your mental maths, do the calculation in your head first and then check it against the meeting ticker). Next time you’re in a meeting that’s going nowhere fast, put the meeting ticker up on the screen and watch how quickly the meeting gets wrapped up! Hopefully it will make managers think twice before they call aimless meetings.

5. Restaurants
It’s often useful to be able to work out percentages and basic addition, subtraction, division and multiplication in your head. Take restaurants, where we add 10% onto the bill for the waitress’ tip. This is something most of us can do in our heads. But what if you are one of three couples at dinner where the bill comes to R817 and you need to split it equally between you? Here’s where mental maths  helps. R817 isn’t divisible by 3. But you could add on an R83 tip (slightly over 10%) to bring the total to R900, and split that easily into R300 per couple.

6. The power of puzzles and brain teasers
Next time you’re in the doctor’s waiting room, instead of checking your Twitter feed, you could solve puzzles and other mental teasers. If crosswords don’t excite you, try some Sudoku puzzles each week. These mental math challenges work like a crossword, except they test your number abilities. To stretch yourself, use different sources (like the daily newspaper or a magazine or online) and push up the difficulty level.

You’ve heard the saying “If you don’t use, you’ll lose it.” Like any other organ in the human body, your brain needs regular exercise to stay sharp. Mental math skills are easy to lose if you don’t  practice. So if you want to go from zero to hero at mental maths, keep at it and in no time, you won’t even need a calculator!