First of all, I will admit that I am not really good at mental math—but I am good enough. Doing mental math was something I practised a lot when I was very young and I can still do things like add a series of numbers or multiply two multi-digit numbers in my head. This helps me make quick calculations before I buy something in a shop. This is particularly important when you are in a foreign country and you are comparing how much it would have cost you back in your country.
For me, I really just work on rounded up figures. For example, if I am asked to add K204 031.01 (about $312) and K79 491 (about $121), I will only round up the figures to the nearest thousand—basically K200 000 (about $306) and K80 000 (about $122). This makes it easy for me to come up with a rough idea of what the total cost is. In this case, I know that the sum will be around K280 000 (about $429) without bogging myself down with the smaller digits.
The thing to keep in mind is that being able to come up with a rough estimate quickly is key. This way, you can do the math in your head while standing on a queue in a shop, giving you time to rethink the whole thing.
Similarly, when you find a shop offering 10 percent discount on their goods/service, then just knock off one zero to the total amount to find the answer. If its five percent, then knock off one zero and divide the answer by two. But what is important is to work with rounded figures not exacts—if you can get the exact amounts, good for you—but not necessary when you are simply comparing prices.
What’s the real benefit for mental math? If you do this type of calculation, you can quickly put your impulse spending in context. Spending K250 000 (about $383) a year on beers and coffee could be half of an extra house plot in a medium or high density location. Owning a house sooner makes it easier and more attainable for you to jump into the career you’ve been dreaming of for years. It might also open the door to having more meaningful investments since your house could be an important collateral, though I only encourage it as a last resort if you only have one house.
If you decide to go ahead with the purchase after doing mental math and weighing the options, that’s great—you will have chosen the option that provides the most value to you. Trust me, a bit of mental math can make all the difference when faced with spending or investment decisions.
If you are too bad at metal maths, then go shopping with your primary school child or the one in your neighbourhood. Oh! Not sure though if this technology-dependent generation will help anyway. Alas! today’s children rely too much on calculators. My free advice to parents and teachers is to snatch away the calculators and encourage the children to do mental math.
Wishing you all a happy New Year. n