Technical Article => Career => Career

Every year, many people will send their resume to Microsoft and Google. So how do these IT companies hire people? What kind of interview questions will they ask. Let's see what Microsoft asked before in this article. These questions are more focusing on how you are reasoning, not necessary your technical skills.



1. 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?

A : Cut the gold bar into one piece, two pieces and four pieces with two breaks, total have 1+2+4=7 pieces.

The first day give work one piece, the second day give two pieces part and get one piece part back, the third day give the one piece part to the worker, the fourth day give the four piece part to the worker and get the two piece and one piece part back, the fifth day give the one piece part and the sixth day give the two piece part and the one piece part back, the last day give the one piece part to the worker. Done.

2. Why is a manhole cover round?

A: Because if it is round, it will not drop down, but if it is square, then from geometry, we know that the diagonal length is larger than the side length, so there is a chance that the manhole cover will drop down.

3. How many cars are there in the USA?

A: We can roughly calculate the cars in USA. We know there are around 400 million people in USA and each family there are 5 people. Then there are 80 million families in USA, We assume that each family has one car, then there are total 80 million cars in USA.

4. How many manhole covers are there in the USA?

A: Similar to above question

5. 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?

A: Unknown



6. 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?

A: The answer is 23.

Common sense first: When a minute hand move around the circle for one lap, it definitely will met once with the hour hand. That means for each hour there will be once and only once overlap for each hour. And also we start from 12 p’clock. So there will be total 23 overlaps in one day.

Calculatetion: Assume the overlapped hour is h and minute is m. Using geometry, when overlapping, the degree of hour hand and minute hand to 12 o’clock marker will be the same. So

(h+ m/60)=m/5=> h=11x/60.Here 0 =<h<23

7. 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.’?

A: Because primes cannot be divided by 2.So if there is a prime pair, then the primes in this prime pair must be odd numbers. So the number between the prime pair must be an even number. So it can be divided by 2.Also, for any consecutive three integers, there always be one integer can be divided by 3.For the prime pair, they can only be divided by 1 and themselves. So only the integer between the prime pair can be divided by 3.Summarize the above two results. The integer can be divided by both 2 and 3.So it should be divided by 6

8. 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?

A: First, switch on one switch for enough long time(maybe 20 minutes),then switch off this switch. Next, switch on another switch, then open the door. The bulb which is lighting is controlled by the switch just be switched on. And also use hands to hold one bulb, if it is cold, the the switch never switched on is to control this bulb.

9. 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?

A: Twice.

First, put three on one side and another three on the other side. If they weigh the same, then the heavier one in the remaining two balls next can find the heavier one in one more measurement.

Second, if the two sides don’t weigh the same, then the heavier on e is in the heavier side. So choose any two of the three balls and put them on the scale. It can be found which one is heavier right now.

10.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?

A: Pick 1 pill from one jar,2 pills from another jar, 3 pills from another jar and 4 pills from the last jar. Then measure the total weight. Check how many more do the pills weigh than the weight if all aren’t contaminated.

Note : I tried to answer some of these questions, if there is any wrong answer, please point it out. I will appreciate it.For question 3 and 4 the answer can be different, as long as you can tell the rationale of the calculation. For question 5, I don't know the answer. Please kindly give the answer if you know. Thank you!

