#### Top Puzzles for Interview with Answer

You are blindfolded and 10 coins are place in front of you on table. You are allowed to touch the coins, but can’t tell which way up they are by feel. You are told that there are 5 coins head up, and 5 coins tails up but not which ones are which.
Can you make two piles of coins each with the same number of heads up? You can flip the coins any number of times.

Flipping Coins Puzzle

A man has 10 bags full of coins. Each bag contains 1000 coins. But one bag is full of forgeries, and he just can’t recall which one. He does know that genuine coins weigh 1 gram, but forgeries weigh 1.1 grams. To hide the fact that he can’t recall which bag contains forgeries, he needs your help.
How can he identify the bag with the forgeries with just one weighing?

Bag of Forgery Coins Puzzle

Suppose we have 3 glasses and 10 coins. The problem is to place odd number of coins in each glass i.e. each glass should contain coins and the number of coins in each glass must be odd and total coins which will be used must be equal to 10.

3 Glass & 10 Coins Puzzle

There are 5 pirates, they must decide how to distribute 100 gold coins among them. The pirates have seniority levels, the senior-most is A, then B, then C, then D, and finally the junior-most is E.

What is maximum amount of coin that Pirate A might get?

What is maximum amount of coin that Pirate A might get?

Pirates and 100 Coins Puzzle

There are 25 horses among which you need to find out the fastest 3 horses. You can conduct race among at most 5 to find out their relative speed. At no point you can find out the actual speed of the horse in a race. Find out how many races are required to get the top 3 horses.

Horse Puzzle

At a party, everyone shook hands with everybody else. And there were no repetition i.e, two same people will not shake their hand twice. There were 66 handshakes. How many people were at the party?

Handshake Puzzle

You have
two ropes.

Each of them burns for one hour. They burn unevenly in different parts though – it means that one half can burn for 20 minutes and other half for 40 minutes. In addition you have a box of matches.

Measure 15 minutes!

Each of them burns for one hour. They burn unevenly in different parts though – it means that one half can burn for 20 minutes and other half for 40 minutes. In addition you have a box of matches.

Measure 15 minutes!

Burning Rope Puzzle

A lady buys goods worth Rs 200 from a shop, whose shopkeeper is selling the goods with zero profit.

- The lady gives him a Rs 1000 note.
- The shopkeeper gets the change from the next shop, keeps Rs 200 for himself, and returns Rs 800 to the lady.
- Later the shopkeeper of the next shop comes with the Rs 1000 note saying “fake note” and takes his money back. How much of a loss did the shopkeeper take?

Shopkeeper & the fake note Puzzle

You have 8 balls all of the same size. 7 of them weigh the same, and one of them weighs slightly more. How can you find the ball that is heavier by using a balance and only two weighings?

Havier Ball Puzzle

You are given four different jars of 2 liters, 4 liters, 6 liters and 8 liters respectively with an unlimited water supply. Then you are asked to measure exactly 5 liters of water using them.

How will you do it?

How will you do it?

5L measuring Puzzle

How many six digit numbers can be formed using the digits 1 to 6, without repetition such that the number is divisible by the digit at its unit place?

6 Digit number Puzzle

You’ve got someone working for you for seven days and a gold bar to pay him. The gold bar is segmented into seven connected pieces. You must give them a piece of gold at the end of every day. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

Gold Bar Puzzle

A bridge will collapse in 17 minutes.

4 people want to cross it before it will collapse. It is a dark night and there is only one torch between them. Only two people can cross at a time.

“A” takes a minute to cross.

“B” takes 2 minutes.

“C” takes 5

and “D” takes 10 minutes

How do they all cross before the bridge collapses?

4 people want to cross it before it will collapse. It is a dark night and there is only one torch between them. Only two people can cross at a time.

“A” takes a minute to cross.

“B” takes 2 minutes.

“C” takes 5

and “D” takes 10 minutes

How do they all cross before the bridge collapses?

Crossing the Bridge Puzzle

You are a prisoner sentenced to death.

The Emperor offers you a last chance to live by playing a simple game.

He gives you 50 black marbles, 50 white marbles and 2 empty bowls.

He then says, “Divide these 100 marbles into these 2 bowls. You can divide them any way you like as long as you use all the marbles. Then I will blindfold you and mix the bowls around. You then can choose one bowl and remove ONE marble. If the marble is WHITE you will live, but if the marble is BLACK you will die.”

How do you divide the marbles up so that you have the greatest probability of saving your life that is choosing a WHITE marble?

The Emperor offers you a last chance to live by playing a simple game.

__GAME-__He gives you 50 black marbles, 50 white marbles and 2 empty bowls.

He then says, “Divide these 100 marbles into these 2 bowls. You can divide them any way you like as long as you use all the marbles. Then I will blindfold you and mix the bowls around. You then can choose one bowl and remove ONE marble. If the marble is WHITE you will live, but if the marble is BLACK you will die.”

How do you divide the marbles up so that you have the greatest probability of saving your life that is choosing a WHITE marble?

Death & Marbles Puzzle

People are waiting in line to board a 100-seat airplane. Steve is the first person in the line. He gets on the plane but suddenly can’t remember what his seat number is, so he picks a seat at random. After that, each person who gets on the plane sits in their assigned seat if it’s available, otherwise they will choose an open seat at random to sit in.
The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?

Airplane Seat Puzzle

There is a building of 100 floors

You’re given 2 eggs.

Find N

How many drops you need to make?

What strategy should you adopt to minimize the number egg drops it takes to find the solution?

- If an egg drops from the Nth floor or above it will break.
- If it’s dropped from any floor below, it will not break.

You’re given 2 eggs.

Find N

How many drops you need to make?

What strategy should you adopt to minimize the number egg drops it takes to find the solution?

2 Eggs & 100 Floors Puzzle

You went to a bank to cash out your cheque.
By mistake the bank cashier gives you-

How much was have you written on cheque ?

- Dollar amount in cent, and
- Cent amount in dollars.

How much was have you written on cheque ?

Bank Cashier Puzzle

A corporate businessman has two cubes on his office desk. Every day he arranges both cubes so that the front faces show the current day of the month.

What numbers are on the faces of the cubes to allow this? Note: You can’t represent the day “7” with a single cube with a side that says 7 on it. You have to use both cubes all the time. So the 7th day would be “07”.

What numbers are on the faces of the cubes to allow this? Note: You can’t represent the day “7” with a single cube with a side that says 7 on it. You have to use both cubes all the time. So the 7th day would be “07”.

Calendar Cube Puzzle

Three ants are sitting at the three corners of an equilateral triangle. Each ant starts randomly picks a direction and starts to move along the edge of the triangle. What is the probability that none of the ants collide?

Ants & Triangle Puzzle

Using only a Four-minute hourglass and a seven-minute hourglass,
How will you measure exactly nine minutes?

Restriction:- Without the process taking longer than nine minutes.

Restriction:- Without the process taking longer than nine minutes.

Measuring 9 mins Puzzle

On a circle there are 2014 light bulbs, 2 are ON, and 2012 are OFF.

You can choose any bulb and change the neighbor’s state i.e. ON to OFF or OFF to ON.

Doing so, What is the maximum number of bulbs we can turn on?

You can choose any bulb and change the neighbor’s state i.e. ON to OFF or OFF to ON.

Doing so, What is the maximum number of bulbs we can turn on?

Bulb in a Circle Puzzle

The owner of a banana plantation has a camel. He wants to transport his 3000 bananas to the market, which is located after the desert. The distance between his banana plantation and the market is about 1000 kilometer. So he decided to take his camel to carry the bananas. The camel can carry at the maximum of 1000 bananas at a time, and it eats one banana for every kilometer it travels.

What is the most bananas you can bring over to your destination?

What is the most bananas you can bring over to your destination?

Camel & Bananas Puzzle

You are the ruler of a medieval empire and you are about to have a celebration tomorrow. The celebration is the most important party you have ever hosted. You’ve got 1000 bottles of wine you were planning to open for the celebration, but you find out that one of them is poisoned.

The poison exhibits no symptoms until death. Death occurs within ten to twenty hours after consuming even the minutest amount of poison.

What is the smallest number of prisoners you must have to drink from the bottles to be absolutely sure to find the poisoned bottle within 24 hours?

The poison exhibits no symptoms until death. Death occurs within ten to twenty hours after consuming even the minutest amount of poison.

What is the smallest number of prisoners you must have to drink from the bottles to be absolutely sure to find the poisoned bottle within 24 hours?

King & Wine Puzzle

Sum Sam and Product Pete are in class when their teacher gives Sam the Sum of two numbers and Pete the product of the same two numbers (these numbers are greater than or equal to 2). They must figure out the two numbers.

- Sam: I don’t know what the numbers are Pete.
- Pete: I knew you didn’t know the numbers… But neither do I.
- Sam: In that case, I do know the numbers.

Sum & Product Puzzle

You are standing before two doors. One of the path leads to heaven and the other one leads to hell. There are two guardians, one by each door. You know one of them always tells the truth and the other always lies, but you don’t know who is the honest one and who is the liar.

You can only ask one question to one of them in order to find the way to heaven. What is the question?

You can only ask one question to one of them in order to find the way to heaven. What is the question?

Heaven or Hell Puzzle

You have 3 jars that are all mislabeled. One jar contains Apple, another contains Oranges and the third jar contains a mixture of both Apple and Oranges.

You are allowed to pick as many fruits as you want from each jar to fix the labels on the jars. What is the minimum number of fruits that you have to pick and from which jars to correctly label them?

You are allowed to pick as many fruits as you want from each jar to fix the labels on the jars. What is the minimum number of fruits that you have to pick and from which jars to correctly label them?

3 Mislablled Jars Puzzle

Two MIT math grads bump into each other at Fairway on the upper west side. They haven’t seen each other in over 20 years.
The first grad says to the second: “How have you been?”
Second: “Great! I got married and have three daughters now”
First: “Really? How old are they?”
Second: “Well, the product of their ages is 72, and the sum of their ages is the same as the number on that building over there..”
First: “Right, ok.. oh wait.. hmm, i still don’t know”
Second: “Oh sorry, the oldest one just started to play the piano”
First: “Wonderful! my oldest is the same age!”
How old are the daughters ?

Ages of the daughters

Given a rectangular cake with a rectangular piece removed.
How can you cut the rectangle in two equal parts with one straight line cut of a knife? (The cut is of any size and any orientation, the removed piece can be one of the layers of the cake)

Rectangular Cake Puzzle

There are two tribes on Mars, the Lie tribe and Truth Tribe. (Lie tribe always speaks lie, True tribe always speaks the truth.)
You meet three mars people and ask –
First Person: What tribe you belong to?
He replies with something in his language which you don’t understand.
Second person – He is saying that he belongs to Lie Tribe.
Third-person – Second person is lying.
What tribe does the third person belong to?

Truth and Lie Puzzle

On Bagshot Island, there is an airport.
The airport is the home base of an unlimited number of identical airplanes.
Each airplane has a fuel capacity to allow it to fly exactly 1/2 way around the world, along a great circle.
The planes have the ability to refuel in flight without loss of speed or spillage of fuel. Though the fuel is unlimited, the island is the only source of fuel.
What is the fewest number of aircraft necessary to get one plane all the way around the world?

Aircraft Puzzle

In a country where everyone wants a boy, each family continues having babies until they have a boy. After some time, the proportion of boys to girls in the country is X: 1.
What is the value of X?

Ratio of Boys and Girls

You are in a dark room where a table is kept.
There are 50 coins placed on the table, out of which 10 coins are showing tails and 40 coins are showing heads.
The task is to divide this set of 50 coins into 2 groups (not necessarily the same size) such that both groups have the same number of coins showing the tails.

Blind Games

There is a bus with 100 labeled seats (labeled from 1 to 100). There are 100 persons standing in a queue. Persons are also labeled from 1 to 100.
People board on the bus in sequence from 1 to n.
The rule is, if a person ‘i’ boards the bus, he checks if seat ‘i’ is empty. If it is empty, he sits there, else he randomly picks an empty seat and sits there.
Given that 1st person picks the seat randomly, find the probability that the 100th person sits in his place i.e. 100th seat.

Chaos in the Bus

A birthday cake has to be equally divided into 8 equal pieces in exactly 3 cuts.
Determine the way this division can be possible.

Birthday Puzzle

There are 2 jugs with 4 litres and 5 litres of water respectively. The objective is to pour exactly 7 litres of water in a bucket.
How can this be done?

Measuring 7 litres

There are 3 switches in a room, where one of them is assigned for a bulb in the next room.
You can’t see whether the bulb is on or off until you leave the room.
Find the minimum number of times you have to go into the room to identify which switch corresponds to the bulb in the other room.

Bulb in the Next Room

The task is to arrange 10 coconuts in 5 lines such that each line has 4 coconuts.

Arranging 10 coconuts

Three people are in a room. Rahul looks at Nisha. Nisha looks at Sahil. Rahul is married but Sahil is not married.
At any point, is a married person looking at an unmarried person?
Three options can be the answer-Yes, No, or Cannot be determined.

Married or Unmarried

You have a bag with 20 blue and 13 red balls.
Your task is to pick two balls in succession.
If the balls are the same colour then you remove them and replace them with a blue ball.
If the balls are of a different colour then you remove them and replace them with a red ball.
What is the colour of the last ball?

Colour of the Last Ball

There are 100 jars each with infinite marbles. All are 10 grams except one jar which has all 9-gram marbles.
How would you find which jar by weighing only once?

Marbles Puzzle

A farmer sold a few chickens to four different customers on a particular day.
It was such that each customer purchased half of the remaining chickens and a half chicken more.
Can you find out how many chickens were sold by the farmer on that day if we tell you that the fourth customer bought a single chicken?

Number of Chicken

There is a square which is made up of four little squares inside it. These squares are made of matchsticks.
Consider you have to remove two matchsticks such that only two squares remain instead of five.

Matchstick Riddle

There are two bottles of 10 liters. Each bottle is completely filled with water.
Now 2 persons having empty bottles of 4 liters and 5 liters want to take 2-2 liters of water.
You can use only these 4 bottles (10 liter-full, 10 liter-full, 5 liter-empty, 4 liter-empty) to transfer the water.
How can this be done?
[Wasting or throwing of water is not permitted]

Taking 2-2 Liters of Water

Vinesh is the fiftieth fastest and the fiftieth slowest runner in his school.
Assuming no two runners are the same speed.
How many runners are in Vinesh’s school?

Runners’ Up

A hen and a half lay one and a half eggs in one and a half-day.
How many eggs does one hen lay in one day?
Also, find how many hens will lay one dozen eggs in 6 days?

The Hen and the Egg

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