Riddles-Microsoft Interview questions
* Why is a manhole cover round?
* How many cars are there in the USA? (A popular variant is "How many gas
stations are there in the USA?")
* How many manhole covers are there in the USA?
* You've got someone working for you for seven days and a gold bar to pay them.
The gold bar is segmented into seven connected pieces. You must give them a
piece of gold 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?
* One train leaves Los Angeles at 15mph heading for New York. Another train
leaves from New York at 20mph heading for Los Angeles on the same track. If a
bird, flying at 25mph, leaves from Los Angeles at the same time as the train
and flies back and forth between the two trains until they collide, how far
will the bird have traveled?
* Imagine a disk spinning like a record player turn table. Half of the disk is
black and the other is white. Assume you have an unlimited number of color
sensors. How many sensors would you have to place around the disk to determine
the direction the disk is spinning? Where would they be placed?
* Imagine an analog clock set to 12 o'clock. Note that the hour and minute hands
overlap. How many times each day do both the hour and minute hands overlap? How
would you determine the exact times of the day that this occurs?
* You have two jars, 50 red marbles and 50 blue marbles. A jar will be picked at
random, and then a marble will be picked from the jar. Placing all of
the marbles in the jars, how can you maximize the chances of a red marble being
picked? What are the exact odds of getting a red marble using your scheme?
* Pairs of primes separated by a single number are called prime pairs. Examples
are 17 and 19. Prove that the number between a prime pair is always divisible
by 6 (assuming both numbers in the pair are greater than 6). Now prove that
there are no 'prime triples.'
* There is a room with a door (closed) and three light bulbs. Outside the room
there are three switches, connected to the bulbs. You may manipulate the
switches as you wish, but once you open the door you can't change them.
Identify each switch with its bulb.
* Suppose you had 8 billiard balls, and one of them was slightly heavier, but the
only way to tell was by putting it on a scale against another. What's the
fewest number of times you'd have to use the scale to find the heavier ball?
* Imagine you are standing in front of a mirror, facing it. Raise your left hand.
Raise your right hand. Look at your reflection. When you raise your left hand
your reflection raises what appears to be his right hand. But when you tilt
your head up, your reflection does too, and does not appear to tilt his/her
head down. Why is it that the mirror appears to reverse left and right, but not
up and down?
* You have 4 jars of pills. Each pill is a certain weight, except for
contaminated pills contained in one jar, where each pill is weight + 1. How
could you tell which jar had the contaminated pills in just one measurement?
* The SF Chronicle has a word game where all the letters are scrambled up and you
have to figure out what the word is. Imagine that a scrambled word is 5
1. How many possible solutions are there?
2. What if we know which 5 letters are being used?
3. Develop an algorithm to solve the word.
* There are 4 women who want to cross a bridge. They all begin on the same side.
You have 17 minutes to get all of them across to the other side. It is night.
There is one flashlight. A maximum of two people can cross at one time. Any
party who crosses, either 1 or 2 people, must have the flashlight with them.
The flashlight must be walked back and forth, it cannot be thrown, etc. Each
woman walks at a different speed. A pair must walk together at the rate of the
slower woman's pace.
Woman 1: 1 minute to cross
Woman 2: 2 minutes to cross
Woman 3: 5 minutes to cross
Woman 4: 10 minutes to cross
For example if Woman 1 and Woman 4 walk across first, 10 minutes have elapsed
when they get to the other side of the bridge. If Woman 4 then returns with the
flashlight, a total of 20 minutes have passed and you have failed the mission.
What is the order required to get all women across in 17 minutes? Now, what's
the other way?
* If you had an infinite supply of water and a 5 quart and 3 quart pail, how
would you measure exactly 4 quarts?
* You have a bucket of jelly beans. Some are red, some are blue, and some green.
With your eyes closed, pick out 2 of a like color. How many do you have to grab
to be sure you have 2 of the same?
* If you have two buckets, one with red paint and the other with blue paint, and
you take one cup from the blue bucket and poor it into the red bucket. Then you
take one cup from the red bucket and poor it into the blue bucket. Which bucket
has the highest ratio between red and blue? Prove it mathematically.