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 Facebook have 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

Question:

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?

Answer:

The answer is 96%.

How:

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

Question:

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?

Answer:

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. You’ll 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

Question:

A snail sits at the bottom of a 30-foot wall.

Each hour it can climb three feet, but it then slips down two feet.

How long does it take the snail to reach the top?

Answer:

The answer is 28 hours.

That’s because for the first 27 hours it climbs a net one foot. But in the 28th hour, it reaches the top with its three-foot climb before having the chance to slide down two feet.

Robert Scott, managing director at Aaron Wallis Sales Recruitment said: “Integrating logic based interview questions into a recruitment process can be a great opportunity to see how a candidate thinks on their feet. It isn’t necessarily about getting the answer right but more of a measure to see how they apply logic and question the information provided.

“Too often interviews rely on evaluating the achievements of a person’s past, which is important, but logic-based questions can be a great indicator of how the candidate deals with the problems that are placed in front of them”

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