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Use your brain instead of your calculator

When taking your numerical reasoning tests, you need to be quick and accurate, two things that don’t necessarily go well together. Having talked to many people about this we have come across a common scenario which costs time and hence, increases the pressure.
 
The main problem is that calculators are used far too often. You need to get used to using your brain rather than tapping away on the buttons. 
 
Every press of a calculator key is an opportunity for a mistake and so the fewer keys that you press, the fewer opportunities there are for errors. Let’s take a look at a typical example and we’ll show you what we mean…
 
Using your calculator
 
Question: What is the percentage increase in total national income in Belgium between 2005 and 2010 if the workforce increased by 100 thousand during that time?
 
Solving this problem is not too difficult. The total national income is the average income multiplied by the size of the workforce. Once we have calculated the two figures then we take the difference and divide by the starting figure (the 2005 value) and multiply by 100. 
 
This might look like this:
 
Calculate 2005 total income:
 
26181 * 3.8 = 99487.8
 
Calculate the 2010 workforce:
 
3.8 + (100/1000) = 3.9
 
Note that we had to adjust the increase figure to make it the same order of magnitude as the workforce figure. Now we can calculate the 2010 total income:
 
28292 * 3.9 = 110338.8
 
Now we can calculate the percentage increase which is:
 
100 * (110338.8 – 99487.8) / 99487.8 = 10.9%
 
As said earlier, the problem is not particularly difficult but there are many opportunities for errors to be induced by "mis-keying" something on your calculator. 
 
Indeed, even while checking the figures for this article we found some mistake on our calculator and had to re-do it to be sure.
 
What can we do about it?
 
Take a look at the overall calculation which is…
 
100 * (28292*(3.8+100/1000) – 26181*3.8) / (26181*3.8) = 10.9%
 
First of all, we should be able to add 100,000 to 3.8 million in our head without having to trouble the calculator. Next, we can see that we have to type in 26131*3.8 twice. So, do this part of the calculation first and store it in the calculator’s memory and then we can reduce the calculation to:
 
‘26181*3.8=MS’
 
‘282982*3.9-MR=/MR*100=’
 
Here we have used MS and MR for ‘memory store’ and ‘memory recall’ and written the order in which you need to type the calculator keys. 
 
Note that you need the ‘=’ after the first MR because you are about to do a divide operation which is a higher priority that the outstanding subtraction and we need to force the subtraction to complete first. We now have fewer keys to press but there is another advantage as well. We now have greater accuracy than doing all the partial calculations and wondering whether to round or not.
 
So the verdict is...
 
Calculators are good in their place but they will only produce results as good as the input that is given to them. Reduce the volume and increase the quality for better results.
 
Wish to practice more numerical reasoning? Check our free numerical demo tests here!
 

 

asd 28 Jul 2015

You have a typo near the end. The extra 8 in 282982.

‘282982*3.9-MR=/MR*100=’

jonathan 27 Oct 2013

nice!

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