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Top 10 Interview Puzzles
Puzzles, riddles, logical questions, and lateral
thinking questions are important part of any
selection process for a job interview.
You can check how good you are by
answering these top 10 interview puzzles.
1. Ant and Triangle Problem
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?
2. Crossing the Bridge Problem
Four people need to cross a rickety bridge at
night. Unfortunately, they have only one torch
and the bridge is too dangerous to cross
without one. The bridge is only strong enough
to support two people at a time. Not all
people take the same time to cross the bridge.
Times for each person: 1 min, 2 mins, 7 mins
and 10 mins. What is the shortest time needed
for all four of them to cross the bridge?
3. Burning Rope Problem
A man has two ropes of varying thickness
(Those two ropes are not identical, they aren’t
the same density nor the same length nor the
same width). Each rope burns in 60 minutes.
He actually wants to measure 45 mins. How
can he measure 45 mins using only these two
ropes.
He can’t cut the one rope in half because the
ropes are non-homogeneous and he can’t be
sure how long it will burn.
4. Heaven’s Gate Probelm
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?
5. 10 Coins Problem
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. How do you make two
piles of coins each with the same number of
heads up? You can flip the coins any number
of times.
6. King and Wind Bottles Problem
A bad king has a cellar of 1000 bottles of
delightful and very expensive wine. A
neighboring queen plots to kill the bad king
and sends a servant to poison the wine.
Fortunately (or say unfortunately) the bad
king’s guards catch the servant after he has
only poisoned one bottle. Alas, the guards
don’t know which bottle but know that the
poison is so strong that even if diluted
100,000 times it would still kill the king.
Furthermore, it takes one month to have an
effect. The bad king decides he will get some
of the prisoners in his vast dungeons to drink
the wine. Being a clever bad king he knows he
needs to murder no more than 10 prisoners –
believing he can fob off such a low death rate
– and will still be able to drink the rest of the
wine (999 bottles) at his anniversary party in
5 weeks time. Explain what is in mind of the
king, how will he be able to do so ?
7. Mislabeled Jar 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?
8. Red and Blue marbles Puzzle
You have two jars, 50 red marbles and 50 blue
marbles. You need to place all the marbles
into the jars such that when you blindly pick
one marble out of one jar, you maximize the
chances that it will be red. When picking,
you’ll first randomly pick a jar, and then
randomly pick a marble out of that jar. You
can arrange the marbles however you like, but
each marble must be in a jar.
9. Gold Bar Problem
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?
10. 100 Doors Puzzle
You have 100 doors in a row that are all
initially closed. you make 100 passes by the
doors starting with the first door every time.
the first time through you visit every door and
toggle the door (if the door is closed, you
open it, if its open, you close it). the second
time you only visit every 2nd door (door #2, #
4, #6). the third time, every 3rd door (door #
3, #6, #9), ec, until you only visit the 100th
door. What state are the doors in after the
last pass? Which are open which are closed?