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Interviews: Off-topic questions

These questions are usually classified as brain teasers, market sizing questions and estimations.

Discover ways to answer them effectively!

What are off-topic questions and which job interviews make use of them?

Off topic questions are usually of the 'how many?' type; for example, "how many vegan restaurants are in L.A?", or "how many trees are there in Redwood forest". They are typically market sizing questions and/or general estimation questions. Brain teasers and puzzles are also not uncommon.

Off-topic questions are usually asked when interviewing for jobs that are intensive in analytic and problem soving skills, for example, in technology, finance, engineering and consulting jobs.

What do interviewers hope to discover?

Interviewers want to discover if you approach topics logically and creatively. They want to ensure that you communicate opinions and solutions eloquently, and persuasively. They want to observe you in brainstorming mode, and they want to know that you can think on your feet.

Emotional responses are also observed; do you retain your confidence levels and do you keep your cool? Do you maintain your reasoning skills?

It really doesn't matter how much you deviate from the correct answer (no one is going to get an exact answer, the interviewers may not know it either). The primary purpose of these topics is to assess your thought processes and temperament.

What skills do they test?

  • Unconventional thinking.

  • Aptitude for solving technical issues and complex problems.

  • Creativity and innovation.

  • Analytical and reasoning skills.

  • Cognitive flexibitlity.

  • Planning.

  • Working memory.

  • Logic and arithmetics skills.

  • Critical thinking.

  • Seeing the big picture.

  • Analyzing data and evaluating options.

  • Thinking on your feet and 'winging it'.

  • Identifying relevent information; sometimes the solution is fairly obvious, but the interviewer wants to know if you have reviewed all the facts and are efficient in identifying pertinent information.

  • Speed in reviewing and retaining information.

Best approach/strategy

Make sure you understand what is being asked, maybe ask to see if there is any more information. The interviewers may actually be waiting to see if you ask for clarification; in addition you will be buying time for your subconscious mind to work on the problem.

Take a moment to consider the question, don't give the first answer that you can think of, instead begin to plan and structure the format to your answer.

Break down a problem into easily estimatable components.

Verbalize the steps that you will be taking, your estimations and assumptions.

Follow through logically, basing your answer on a logical sequence of events, logical assumptions and estimates.

Even though your overall speed may be evaluated, it is still much better to take your time.

Remember that the emphasis should be on your approach, and thought process, and not the final answer.


  • Realize that there is no right or wrong answer to some of these questions. There are many things being tested, and sometimes a precise answer isn't so important.

  • When confronted with something totally unfamiliar stay calm, the interviewers expect you to take time to consider your response.

  • If you feel more comfortable with a pen and paper find out if they are permitted.

  • Listen carefully.

  • Any answer is better than none, provide any reasonable response.

  • For market-sizing and estimation questions use round numbers so you can get an estimate quickly and without errors.

Questions types

It is possible to decode the types of off-topic questions by grouping them. This will enable you to place a question quickly.

Market sizing questions

It is best to use a predifined format for answering both the market sizing and estimation questions. Making a plan will typically involve categorizing correct components, and solving each component separately. Make sure that you know the correct components by asking the iterviewers for help. Basing your calculations on accurate assumptions can only serve to boost your confidence. For example, if you are asked to estimate the world market for ice cream ask to see if sorbet and popsicles are included in the definition.

Example questions.

Example1: How many people wear ties in London on a weekday?

Start by establishing the correct parameters. Is this the city of London we are talking about or the entire London area. Do 'neckties' include bolo Ties, bowties, neckerchiefs, and cravats? Is this during summer or winter?

Let's assume that you have agreed with your interviewers that London covers the whole of London, in the winter, and that 'neckties' only include classical neckties.

You will need to estimate the following: Population of London. Percentage of adults wearing neckties on a weekday and percentage of minors wearing neckties.

One way to go about it would be to estimate the percentage of adult men of working age, and how many of them wear neckties at work. Decide whether it is worth calculating the neckties worn by adult men that are not of working age, during the day.

Estimate the percentage of adult women of working age, and how many of them wear neckties to work.

Estimate the percentage of school children, and how many wear neckties to school.

Example2: What’s the market size for electric cars in Belgium?

Clarify concepts such as whether electric cars inlcude hybrid vehicles.

Define how the market is defined and measured. Make sure that the market covers everyone inluding individuals, companies, taxi cabs, and government agencies. It is reasonable also to assume that the market is measured in annual revenue sales.

Estimate the population of Belgium to be 10 million.

Break down the market into meaningful segments. For example, first time buyers and owners seeking to replace their electric cars.

First time buyers: If the life expectancy is 80 years then every year there are 125,000 eligible first time buyers, assuming people's ages are evenly distributed. Assume 15% will actually buy a car, (18,750 cars). Assume 4% buy an electric car. This is 750 cars.

Owners seeking to replace their cars: Assume that 30% of the population already own a car and that the economic useful life of a car is 8 years. This means 375,000 cars are up for replacement. Assume a 3% replacement rate, slightly less than first time buyers due to people's attachments with their previous cars. This is 11,250 cars.

We have generated a total of 12,000 electric cars. If we assume an average price of $20,000 per car, then the total market size for electric cars in Belgium is $240M

Example:How much would a Tokyo coffee house bring in, in annual revenue?

Factors to consider: Average ticket cost, average traffic per day.

Example: How much many oranges are sold in Ralphs supermarkets, in California, every year?

Factors to consider:

Estimate how many kilos are sold every day in each supermarket

If the supermarkets makes fruit juices estimate how many kilos of oranges are used to prepare drinks.

Example: How many bowling balls are there in Paris?

Factors to consider:

Percentage of Parisiennes that bowl.

Estimate the number of bowling halls in Paris.

Estimate how many people own their own bowling ball, and how many use the ones provided in the bowling halls.

Estimate how many bowling balls a bowling hall should have and how often they need to be replaced.

Example: How many car washes are there in the Sweden?

Factors to consider:

Estimate how many car washes there are per 100,000 people.

More examples..

How many gallons of bottled water are sold in the United States each year?

How many square feet of pita bread are eaten in the United States each month?

How many boxes of chewing gum are sold in the US every year?

Estimation questions

Example: How many street lights are there in the U.K?

Over 7.5 million streetlights.

Source: Highways term maintenance association U.K.

Example: How many times heavier than a house cat is a tiger?

200 times.

A tiger can weight up to 300kg.

Example: How many fire runs were made by the Tokyo fire department in 2008?


Source: Wikipedia.

Example: How many trees are there on planet earth?

3 trillion.

Source: Yale University.

Example: How many tennnis balls will fit into a 65 square metre room that is 2.5 metres high?

Over a million.

Example: What is the weight of a commercial aeroplane?

Airbus A340-500.

Maximum take-off weight: 371 metric tons.

Maximum landing weight: 240 metric tons.

Practical questions

Example: Why is it better to have round manhole covers than square ones?

A round manhole cannot be dropped down the manhole.

Example: How can you tell if the light inside your refrigerator is on or not?

Record inside with your cell phone

Example: How would you determine the weight of a commercial airplane without a scale?

Using tire pressure and tire displacement.

Insignificant details

Make sure that the question isn't just a facade, and you overlook fairly obvious, important information.

Identifying relevent information; sometimes the solution is fairly obvious, but the interviewer wants to know if you have reviewed all the facts and are efficient in identifying only the pertinent information.

Example: Sarah's mother had four children. One child was name April. The second one is May. The third is June. What‘s the fourth one’s name?


Example: An electric train is traveling on a 3000-mile journey from Slovakia to Paris. It has 46 cars with a total of 500 passengers. It's in the middle of June and the passengers are all drinking sodas. Which direction will the steam blow?

It's an electric train.

Outside the box

At first sight these questions seem like impossible situations with no possible answer, however commit yourself to finding an answer and you could find yourself stepping into a realm of unconventional thinking.

Example: A woman and a daughter walked into a restaurant. A man walked past and the women both said, “Hello, Father”. How is this possible?

The man was a member of the clergy.

Example: Two mothers and two daughters sit down to have luinch. They ate three breadsticks and each person at the table ate a breadstick. Explain how.

One of the mothers is also a grandmother.

Example: An apple costs 40 cents, a banana costs 60 cents, and a grapefruit costs 80 cents. How much does a pear cost?

40 cents. Assign 20 cents per vowel to each word.


These questions make use of multiple word meanings. If something doesn't seem to make sense no matter how many possible scenarios you imagine, try switching the meanings of words.

Example: What two words, when combined, hold the most letters?

Post office, or post box.

Example: You walk across a bridge and you see a boat full of people yet there isn’t a single person on board. Why is this?

They're all married.


Identify the next item in a list.

Example: 4 5 8 17 44


Example: 13 57 911 1315 1719



Example: There is a waterlily in a pond, that doubles in size every day. If it takes the waterlily 10 days to cover the entire pond, how long does it take to cover half the pond?

9 days

Example: You are in a race and you overtake the person who is in fourth place. What is your position now?



Example: A tennis racket and duffle bag cost $140 in total. The racket costs $100 more than the bag. How much does the bag cost?


Example: You begin reading a book 40 pages long. If you read half of the remaining book each day how long would it take you to finish the book?


Example: What is the decimal equivalent of 10/16?


Example: How can you add eight eights and reach 1000?

888 + 88 + 8 + 8 + 8 = 1,000


Example: What does the following represent? COF FEE

Coffee break

Example: What does the following represent? SYMPON

Unfinished symphony.

The philosopher

Example: How do you know if anything your brain is comprehending is real - could it all just be in your brain?

You're on your own here!

The riddler

Example: What is it that goes with an automobile and comes with it; is of no use to it, and yet the automobile cannot move without it?


Example: What has no content yet you can see it?

A hole.