﻿ What Usain Bolt and Psychometric test success have in common: Speed

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# 14 Dec 2012 Print What Usain Bolt and Psychometric test success have in common: Speed

What Usain Bolt and Psychometric test success have in common: Speed

This isn’t the first time I’ve written about estimating answers in psychometric tests and, I daresay, it won’t be the last.

This is because it is important – in fact, essential. Usain Bolt has won several Olympic medals by being extremely fast... and you can win a new job by being sufficiently fast to beat most other candidates.

2 minutes have never felt so quick

You have about 2 minutes per question and in that time you have to read the question, assimilate the data, decide on the method of solution and then, finally, do the calculation. Even the relatively easy questions are difficult with this kind of time pressure. You need some shortcuts and estimation is a very useful one at that.

Q. Which country had the smallest percentage growth in households with 2+ cars between 1990 and 2005?

How did you do?

Let’s go through it together…

Step 1. Read the question. The question is straightforward enough but note that it asks for the smallest rather than the largest – we don’t want to be calculating the wrong thing – and it asks for the percentage growth which is not the same as the increase in percentage points. This is a common trap but I won’t labour it here as it isn’t the point of this article (see more on percentage points here).

Step 2. Assimilate the data. Look at the data table and understand what it is that you are being shown. Column 2 shows the percentage of households in 1990 that have two or more cars and column three shows the same thing for 2005.

Step 3. Decide on the method of calculation. This is a relatively common type of question so you should be familiar with the method of solution. The growth between two numbers is the difference divided by the starting point and then multiplied by 100 to make it a percentage. We can omit the last step of that since we are only comparing values between each country and we are not interested in the magnitude of the growth.

Step 4. Do the calculation. At this point you can use your calculator to do the four calculations and decide which one is lowest. However, I did say that you were not allowed to use a calculator and the theme of this article suggests that there might be an easier way.

The difference between the two figures is quite easy to do in your head but then dividing this number seems to be not quite so easy. Let’s take a look at Belgium. The difference is (16.3-14.8=1.5) so it grew by 1.5 percentage points from a base of 14.8 and so the proportional increase is 1.5/14.8 which is very close to 1/10 or 10% but just a little over.

Now we can do the same for the other countries and we end up with fractions:

All of these are within a gnat’s whisker of 1/10 but only one of them is just under 1/10; the other three are just over 1/10. Now, if the question had asked which country had the highest growth then that would have been a much more difficult call.

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### Coach28 Jan 2013

Kassra,

You are indeed correct that there is a mistake. The mistake is actually in the data and the value for Spain in 2010 should have been 15.2. I'm tempted to say that I put the error in deliberately to see if you were paying attention but I hold my hands up - I didn't check my work thoroughly enough. Sorry about the confusion caused and well done for spotting it.

### Kassra25 Dec 2012

Thanks. That was a very helpful article. Is there not a mistake here above the last paragraph, where the fractions are written? I believe the last fraction should be 0.4/13.8 and now 1.4/13.8. (14.2-13.8=0.4)

That would make Spain the correct answer and not France.

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