Brain Teaser

Interviewers ask brainteaser questions because they think your ability to answer will provide some indication of your ability to do the job. Often, the hiring manager feels the brainteaser will help them to evaluate your strength in one or more of the following competency areas:

• Problem solving — Can you quickly analyze a problem and devise a solution?
• Critical thinking — Can you see the big picture, think clearly, evaluate options?
• Analytic skills — Can you analyze data, determine probability, make calculations?
• Creativity — Do you take an innovative approach to problems?
• Ability to think on your feet — Can you “wing it” without preparation or structure?
• Ability to perform under pressure — Can you stay cool and logical under stress?

Recruiters often use brainteaser questions for recent college graduates to understand their critical thinking process.

The interviewer is most interested in your approach to the brainteaser and how you think. The actual answer is often irrelevant.

How to answer brain teaser questions:

1. Take a moment to carefully consider the question. Don’t feel like you have to blurt out the first answer that comes to mind.

2. Ask any clarifying questions. Make sure you understand the question and what the interviewer is looking for. See if there is additional information available.

3. Walk-through your thinking process out loud. Verbalize the steps you would take to solve the brainteaser and, if relevant, the data that you would need (making estimates and assumptions if necessary). Put the emphasis on your approach, not on the final answer.

1. The “How many?” Brainteaser

Here is a classic brainteaser beloved by interviewers:

“How many gas stations are there in the U.S.?”

Other variations include:
• “How many barbers are there in Chicago?”
• “How many piano tuners are there in New York?”
• “How many boxes of breakfast cereal are sold in the U.S. each year?”
• “How many golf balls will fit inside a Boeing 747?”

These questions (and the many other adaptations) ask the candidate to think through a problem.

For this brainteaser, start estimating for a small-town population and then move up from there. e.i one gas station for 10000 people and do the math for how many for total population of the US.

2.Three light bulbs and switches in a room

A windowless room contains three identical light fixtures, each containing an identical light bulb or light globe. Each light is connected to one of three switches outside of the room. Each bulb is switched off at present. You are outside the room, and the door is closed. Before opening the door you may play around with the light switches as many times as you like. But once you’ve opened the door, you may no longer touch a switch. After this, you go into the room and examine the lights. How can you tell which switch goes to which light?

– Turn on switch number 1, wait a moment and turn off switch number 1.
– Turn on switch number 2.
– Enter the room. Whichever bulb is on, it is wired to switch 2.
– whichever is off and hot is wired to switch number 1.
– and the third is wired to switch 3.

Another form of this puzzle sets up that you are renovating a building or something like that. There are three switches in the basement, two of which are useless, one is connected to a lightbulb in the attic. You must determine which needs saving and remove the other two. It’s basically the same solution as our first idea. That is switch on 1&2, wait a minute, switch off two and go to the attic and check if the bulb is on, hot, or cold.

3. Measuring Water with no scales

Let’s say you have a 3-gallon bucket, a 5-gallon bucket, and an infinite amount of water. These two buckets don’t have any scales. How would you measure exactly 4 gallons?

Solution #1

1. Fill up the 3-gallon bucket

2. Empty it into 5-gallon bucket

3. Fill up, again, the 3-gallon bucket

4. Pour 2 gallons into the 5-gallon bucket to fill it up. By doing this, the 3-gallon bucket will have exactly 1 gallon in it.

5. Empty the 5-gallon bucket.

6. Empty the 1 gallon (from the 3-gallon bucket) into the 5-gallon bucket.

7 Fill the 3-gallon bucket and empty it into the 5-gallon bucket.

8. The 5-gallon bucket now has 4 gallons of water in it.

Solution #2

1. Fill up the 5-gallon bucket.

2. Using the 5-gallon bucket, fill up the 3-gallon bucket. By doing this, the 5-gallon bucket now has 2 gallons in it.

2. Empty the 3-gallon bucket.

3. Empty the 5-gallon bucket (2 gallons in it) into the 3-gallon bucket.

4. Fill up, again, the 5-gallon bucket.

5. From the 5 gallon bucket, Pour 1 gallon into the 3-gallon bucket to fill it up.

6. The 5-gallon bucket now has 4 gallons of water in it.

4. Why are manhole covers round?

Because the round shape is the only shape that cannot fall through a whole of its shape.

5. Trail by bikes

There are 50 bikes with a tank that has the capacity to go 100 km. Using these 50 bikes, what is the maximum distance that you can go?

Solution #1

All bikes take off for 50 km. Half of bikes (50/2=25) empty their tank to the other 25 bikes to fill them up. Do this again for another 50 km and half of bikes empty their tank to the other and now you are down to 12.5 bikes. Do it again for another 50 km and you are down to 6.25 bikes. Do it again for another 50 km and you are down to 3 bikes. Do it again for another 50 km and you are down to 1.5 bikes. Do it again for another 50 km and you are down to half a tank. That half a tank for the last bike goes for 50 km. So the answer is 350 km.

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Brain Teaser

September 23, 2019