Do not be afraid to do simple sums for yourself

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

27 November 2022

Sometimes I get questions that give me the impression that people fear doing simple sums for themselves. After the announcement that Kenya will start buying electricity from Ethiopia at the price of 6.50 US cents per unit (kilowatt-hour), a reader asked me how much this was in Kenyan shillings. My first assumption was that the reader didn’t know how many US cents make a US dollar, so I replied informing him that US$1 = 100 US cents.

I thought that, with that information, he could do the rest of the calculation. But I was shocked when he responded with this: “so, US$1 = 100 US Cents; 6.50 US Cents =? Kenya shillings. That's where am stuck.” So, I sent him this: “$1 = 100 US cents = Sh122; So, 1US cent = Sh1.22”. Now he was able to work it out; that is, 6.5 US cents = 1.22 x 6.5 = Sh7.93, or, approximately Sh8.

I suspect that the reader had probably done this math a few times over but found it hard to believe the answer. Perhaps because he probably knows how much consumers pay for electricity (Sh25). Still, there is an underlying problem as the following second encounter illustrates.

Recently, I had a dispute with a salesman at a floor tile dealers’ shop about the diagonal of square tiles. The product in question measured 40cm by 40cm. The salesman insisted that a half of its diagonal is 20cm!

I told him it cannot be 20cm but he was sure of this that he was willing to bet of Sh1,000 on it! When I told him to remember the Pythagoras theorem from school, he retorted: “this is not scientific theory; it is practical life!” Well, I asked him to get his calculator and do the following sum…40cm squired; multiplied by two; and then find the square-root. Finally divide the square-root by two. The answer came to 28.3cm.

I told him that this is the size of half of the diagonal. But he still stood his ground. So, I asked him to bring out his measuring tape and we measured the disputed length. He was so shocked by the answer that he repeated the measurement several times in utter disbelief!

We joked about it, but, as I left the shop, I was disturbed. Why are so many people not convinced that what they learn in school is actually true in real life? Well, that discussion is outside the scope of this column.