1. 10 Famous Microsoft Interview Puzzles
Here is a list of 10 famous puzzles which have been asked on a Microsoft Interview. They are not in any
specific order.
Clock Hands
How many times a day do the minute and hour hands of a clock overlap? Answer
Is Your Husband a Cheat?
A certain town comprises of 100 married couples. Everyone in the town lives by the following rule: If a
husband cheats on his wife, the husband is executed as soon as his wife finds out about him. All the
women in the town only gossip about the husbands of other women. No woman ever tells another
woman if her husband is cheating on her. So every woman in the town knows about all the cheating
husbands in the town except her own. It can also be assumed that a husband remains silent about his
infidelity. One day, the mayor of the town announces to the whole town that there is at least 1 cheating
husband in the town. What do you think happens? Answer
100 Prisoners in Solitary Cells
100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and
offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be
selected more than once), into a special room with a light bulb and a switch which controls the bulb. No
other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the
bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say “Every
prisoner has been in the special room at least once”. If that happens to be true, all the prisoners will be
set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss
and figure out a solution. How do they ensure they all go free? Answer
The Ant Problem
2. 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? Answer
Gold for 7 days of Work
You’ve got someone working for you for seven days and a gold bar to pay them. You must pay the
worker for their work at the end of every day. If you are only allowed to make two breaks in the gold
bar, how do you pay your worker? (Assuming equal amount of work is done during each day thus
requiring equal amount of pay for each day) Answer
Trains and Birds
A train leaves City X for City Y at 15 mph. At the very same time, a train leaves City Y for City X at 20 mph
on the same track. At the same moment, a bird leaves the City X train station and flies towards the City Y
train station at 25 mph. When the bird reaches the train from City Y, it immediately reverses direction. It
then continues to fly at the same speed towards the train from City X, when it reverses its direction
again, and so forth. The bird continues to do this until the trains collide. How far would the bird have
traveled in the meantime? Answer
A Box of Defective Balls
You have 10 boxes of balls (each ball weighing exactly10 gm) with one box with defective balls (each one
of the defective balls weigh 9 gm). You are given an electronic weighing machine and only one chance at
it. How will find out which box has the defective balls? Answer
Globe Walker
How many points are there on the globe where, by walking one mile south, then one mile east and then
one mile north, you would reach the place where you started? Answer
3. 4 Quarts of Water
If you had an infinite supply of water and a 5 quart and 3 quart pails, how would you measure exactly 4
quarts? and What is the least number of steps you need? Answer
Four People on a Rickety Bridge
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? Answer
