Brain Teasers

Question 1

Are you exhaling warm air?

Answer 1

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Question 2

Explain quantum electrodynamics in two minutes, starting now.

Answer 2

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Question 3

Given 20 ‘destructible’ light bulbs (which breaks at certain height), and a building with 100 floors, how do you determine the height that the light bulb breaks?

Answer 3

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Question 4

Given a dictionary of words, how do you calculate the anagrams for a new word?

Answer 4

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Question 5

Given the numbers 1 to 1,000, what is the minimum number of guesses needed to find a specific number, if you are given the hint ‘higher’ or ‘lower’ for each guess you make?

Answer 5

This is called binary search. Given an interval [a,b], your guess should be the middle element i.e. (𝑎+𝑏)/2 at each step. If your guess is right, then great! Otherwise, you should adjust your bounds of your current interval. If that specific number is “higher”, your new interval will be [(𝑎+𝑏)/2 +1,𝑏]. Similarly if it is “lower” then your new interval will be [𝑎,(𝑎+𝑏)/2−1]. You will keep guessing until the lower bound is greater than the upper bound, in other words, until your interval collapses.

Question 6

How are M&M’s made?

Answer 6

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Question 7

How many ball bearings, each one inch in diameter, can fit inside a 747 aircraft?

Answer 7

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Question 8

How many bottles of beer are drank in the city over the week.

Answer 8

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Question 9

How many bricks are there in Shanghai? Consider only residential buildings.

Answer 9

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Question 10

How many cows are in Canada?

Answer 10

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Question 11

How many hair salons are there in Japan?

Answer 11

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Question 12

How many people are using Facebook in San Francisco at 2:30 pm on a Friday?

Answer 12

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Question 13

How many planes are currently flying over Kansas?

Answer 13

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Question 14

How many quarters would you need to reach the height of the Empire State building?

Answer 14

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Question 15

How many ridges are there around a quarter?

Answer 15

119 (they’re also called reeds)

Question 16

How many smartphones are there in London?

Answer 16

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Question 17

How many times a day do a clock’s hands overlap?

Answer 17

22 times (every 65 minutes)

Question 18

How many traffic lights are there in Manhattan?

Answer 18

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Question 19

How much money did residents of Dallas/Ft. Worth spend on gasoline in 2008?

Answer 19

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Question 20

How would you measure 9 minutes using only a 4 minute and 7 minute hourglass?

Answer 20

Flip both timers over. When the 4-min timer is empty, flip it over (the 7-min timer has 3 minutes left in the top). When the 7-min timer is empty, flip it over (there is now 1 minute left in the top of the 4-min timer). When the 4-min timer is empty for the second time, the 7-min timer has 1 minute worth of sand in the bottom half. Flip it over so there is now 1 minute in the top. When the 7-min timer empties, 9 minutes have elapsed.

Question 21

If two cars are travelling in a two lap race on a track of any length, one going 60 mph and the other going 30 mph, how fast will the slower car have to go to finish at the same time as the faster car?

Answer 21

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Question 22

If you had 5,623 participants in a tournament, how many games would need to be played to determine the winner?

Answer 22

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Question 23

If you won the lottery, what would you do with the money?

Answer 23

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Question 24

Out of 25 horses, pick the fastest 3 horses. In each race, only 5 horses can run at the same time. What is the minimum number of races required?

Answer 24

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Question 25

What is the probability of throwing 11 and over with two dice?

Answer 25

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Question 26

What is the temperature when it’s twice as cold as zero degrees?

Answer 26

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Question 27

What should it cost to rent Central Park for commercial purposes?

Answer 27

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Question 28

What were the causes of the First World War?

Answer 28

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Question 29

When a hot dog expands, in which direction does it split and why?

Answer 29

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Question 30

Why are manhole covers round?

Answer 30

A round manhole cover can't fall through the round manhole opening. A square cover, on the other hand, could fit diagonally through the opening and fall through. Additionally, a circular cover fits easily, and can be removed easily, without much precision or rotating.

Question 31

You are given 2 eggs, you have access to a 100-story building.  Eggs can be very hard or very fragile which means they may break if dropped from the first floor or may not even break if dropped from the 100th floor. Both eggs are identical. You need to figure out the highest floor of a 100-story building an egg can be dropped without breaking. The question is how many drops you need to make. You are allowed to break 2 eggs in the process.

Answer 31

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Question 32

You are in a dark room with no light. You need matching socks for your interview and you have 19 gray socks and 25 black socks. What are the chances you will get a matching pair?

Answer 32

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Question 33

You have 8 pennies, 7 weight the same, one weighs less. You also have a judges scale. Find the one that weighs less in less than 3 steps.

Answer 33

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Question 34

You have a birthday cake and have exactly 3 slices to cut it into 8 equal pieces. How do you do it?

Answer 34

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Question 35

You have a bouquet of flowers. All but two are roses, all but two are daisies, and all but two are tulips. How many flowers do you have?

Answer 35

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Question 36

You have five bottles of pills. One bottle has 9 gram pills; the others have 10 gram pills. You have a scale that can be used only once. How can you find out which bottle contains the 9 gram pills?

Answer 36

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Question 37

You have three boxes. One contains only apples, one contains only oranges, and one contains both apples and oranges. The boxes have been incorrectly labeled so that no label accurately identifies the contents of any of the boxes. Opening just one box, and without looking inside, you take out one piece of fruit. By looking at the fruit, how can you immediately label all of the boxes correctly?

Answer 37

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Question 38

You're in a row boat, which is in a large tank filled with water. You have an anchor on board, which you throw overboard (the chain is long enough so the anchor rests completely on the bottom of the tank). Does the water level in the tank rise or fall?

Answer 38

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