HR 12 September 2018

3 logic-based interview questions to help you find the brightest candidates

logic-based questions
Companies like Google and Facebook regularly use logic-based interviews to assess candidates
Logic-based interview puzzles are becoming increasingly popular in recruitment processes to help employers find the brightest candidates and gain insight into a candidate’s thought process.

Brain teasers are particularly popular in the tech sector, where employers want to find the most logical candidates who can help them advance with their next innovative product launch.

Famously, Google is very keen on logic puzzle interview questions, even ceasing to ask some of their more difficult questions as they were too tricky?. More recently, tech giants like Airbnb and Facebookhave adopted logic puzzle questions to find the right software developers to keep them ahead of the competition.

With this in mind, Aaron Wallis Sales Recruitment has collated a series of three great logic-based interview questions for employers to work into their recruitment processes:

  1. Newcastle rain


you’re about to board a train from London to Newcastle.

You want to know if it’s raining, so you call your three friends who live in Newcastle.

Each friend has a 2/3 chance of telling you the truth and a 1/3 chance of telling you a lie.

All three friends tell you that, yes, it’s raining in Newcastle.

What is the probability that it is, in fact, raining in Newcastle?


The answer is 96%.


You only need one friend to be telling the truth. So if you calculate the odds of them all lying, that’s 1/3 multiplied together, making 1/27 (1/3 x 1/3 x 1/3).

So that’s a 1 in 27 chance that all of your three friends are lying. So, switch that around, and it’s a 26/27 chance one of them is telling the truth or 96% that it is, indeed raining in Newcastle.

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  1. Juggling jugs


You have a 5-litre jug and a 3-litre jug. That’s great, but how would you measure out exactly 4 litres without using any other equipment?


First, fill the 3-litre jug and pour it into the 5-litre jug. The 3-litre jug is now empty, and the 5-litre jug has 3 litres in it.

Now, fill the 3-litre jug again and tip it slowly into the 5-litre jug. Youll have 2 litres in before the 5-litre jug is full because it already has 3 litres in from before?

Now you have 1 litre left in the 3-litre jug and the 5-litre jug is full.

Empty the 5-litre jug. Now pour the remaining 1 litre in the 3-litre jug into the 5-litre jug.

Lastly, fill up the 3-litre jug again and tip it all into the 5-litre jug, which now ends up with exactly four litres in it!

    1. Snail trail