WTDTYIS1:Real mathematics for real life situations

( The "What They Don't Teach You In School" series tries to dispel the fear of mathematics from the minds of the readers. )

Most people do not check whether the total bill amount is correct or not at stores. Even if some do, they take out their mobiles and click on the calculator application.

And this is not good - not good at all.

Researches have shown the more we depend on technology unnecessarily, and the less we use our brains, the more the chances are that we will have alzheimer's or other mental illnesses in the coming days.

Now think of a knife. It will capture rust and lose its sharpness if you do not use it. Same goes for the human brain - the most sophisticated organ in our body. Daily mental exercises are, perhaps, even more important than physical ones - and mental alertness is no less valuable than physical fitness.

Let us take previous weekend's incident to illustrate the importance of mental training.

I went to the supermarket and was looking for probiotic dahi ( uk : curd / usa : yogurt ). They were available in different quantities. The first thing was required is to generate comparable values. I can never compare the prices of a 200 grams probiotic dahi of ABC brand to that of a 350 grams of XYZ. Which means I need to find out the rate of each product in kilograms.


A 400 grams amul probiotic dahi costs 35 bucks. To find its rate in kilograms we need to find the cost of 100 grams and then multiply it by 10. But 35 is not completely divisible by 4. So - what we need to do? We will round it ( upwards or downwards depending upon the convenience ) to the next available number which will leave no leftover after a division by 4 - and the number is 36 in this case.

Hence, 100 grams amul probiotic dahi costs 9 ( 36 / 4 ) bucks and a kilogram costs 90 ( 9 * 10 ). But we should not forget about the extra 1 that we added to 35. Again, 1 divided by 4 is 0.25 and 10 times 0.25 is 2.5. Finally - if we subtract 2.5 from 90 we get 87.5 and which is the actual ( ie not approximated ) cost of the amul probiotic dahi per kilogram.

[ Had the price of 400 grams amul probiotic dahi been 41, we would have then subtracted 1 from 41 and then add 2.5 ( ( 1 / 4 ) * 10 ) to 100 ( ( 40 / 4 ) * 10 ), which makes the final result 102.50 - the actual cost of amul probiotic dahi per kilo. ]

This technique needs to be repeated to find out the rate per kilo for probiotic dahis of other brands and then we will have a handful of comparable values. And just like anything else, this trick needs too a little practice and after a while whenever you will see values you will start computing them spontaneously and in no time.

That's all for now. Stay tuned for yet another trick in the WTDTYIS series which will make your brain healthier and your life simplified.

( Photo by Anand Milk Union Limited. Brand information : AMUL is the world's largest producer of milk and dairy products and also the inventor of India's first milk-atm. )