Here are some interview questions asked at Google and Microsoft. Some of these are supposed to generate a specific answer, some are asked to gauge how you estimate, analyse and approach the seemingly impossible problems.

Post some of your answers in the comments, but no cheating. I’ve figured out number 10, but would be interested in your solutions.Number 11 has me puzzled, and if you can do number 13, then I think you **own** Google. And I would love to hear your answers to number 16 and number 17.

(All of the questions below were harnessed from websites and blogs about Google and Microsoft, and all were supposedly asked of someone, at some point. But no guarantees.)

1. How many golf balls can fit in a school bus?

2. How much should you charge to wash all the windows in Seattle?

3. Explain a database in three sentences to your eight-year-old nephew.

4. How many times a day do a clock’s hands overlap?

5. You have to get from point A to point B. You don’t know if you can get there. What would you do?

6. Imagine you have a closet full of shirts. It’s very hard to find a shirt. So what can you do to organise your shirts for easy retrieval?

7. In a country in which people only want boys, every family continues to have children until they have a boy. if they have a girl, they have another child. if they have a boy, they stop. what is the proportion of boys to girls in the country?

8. You are at a party with a friend and 10 people are present including you and the friend. your friend makes you a wager that for every person you find that has the same birthday as you, you get $1; for every person he finds that does not have the same birthday as you, he gets $2. would you accept the wager?

9. How many piano tuners are there in the entire world?

10. You have eight balls all of the same size. Seven 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?

11. You have five pirates, ranked from five to one in descending order. The top pirate has the right to propose how 100 gold coins should be divided among them. But the others get to vote on his plan, and if fewer than half agree with him, he gets killed. How should he allocate the gold in order to maximise his share but live to enjoy it? (Hint: One pirate ends up with 98% of the gold.)

12. 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 travelled?

13. 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 six (assuming both numbers in the pair are greater than six). Now prove that there are no “prime triples”.

14. 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?

15. How would you build an alarm clock for deaf people?

16. If Microsoft told you we were willing to invest $5-million in a start-up of your choice, what business would you start? Why?

17.If you are going to receive an award in five years, what is it for and who is the audience?

18. Suppose you go home, enter your house/apartment, hit the light switch, and nothing happens — no light floods the room. What exactly, in order, are the steps you would take in determining what the problem was?

1. Zero. VW Golf’s are cars and cars are female. and thus don’t have balls.

2. Nothing. Microsoft, the creator of Windows is based in Seattle. As Windows is proprietary, you can’t wash them. Only Microsoft can and updates are free.

3. Assuming he could play Tic-Tac-Toe, I’d use it as an example to explain rows and columns and teach him to play it blind-folded.

4. 23

5. Use references instead of pointers.

6. Take them out of the closet and spread them on the floor. Instant visual recognition. No-one has time for sorting shirts if they need to write complex sorting algorithms.

7. Half of the couples will have a boy on the first try and will stop. Half of the 2nd half will have a boy on the 2nd try and then stop. Half of this half will have a boy on the 3rd try and stop. And so on. Assuming a 100 couples: 50 boys + 50 girls + 25 boys + 25 girls and so on… The ratio is 1:1.

8. No. Being at a party I’m already somewhat intoxicated. I don’t need to think about this one statistically. My friend is making the wager and he expects to win it, no matter what the actual wager is.

9. 1 in every 10 of my friends growing up had a piano in their home. Assuming 2 million middle-class families in South Africa, that’s 200,000 pianos. Assuming the average piano is tuned every 5 years, and a piano tuner can visit 2 families a day, he’d tune roughly 600 pianos a year. There are 40,000 pianos that need to tuned each year in SA alone. Just more than 60 tuners will do the trick for this country. Assuming SA is a good mean (more middle-class citizens than other African countries, but less than India, Europe, Oceania or the US), we would need 6 billion / 50 million * 60 tuners = 72,000 tuners.

10. Remove 2 balls. Weigh 3 vs 3. If equal, remove the 6 balls, and weigh the 2 you removed earlier against each other. If unequal, take the heavier 3 balls and throw away the rest. Now put one aside and weigh 1 vs 1. If equal, the one aside is the heavier.

Okay, that was an entertaining 15 minutes… Will attempt the rest later!

4. 25, not 23…

Henk, Google called. They have another question: when can you start?

11. If the top pirate gets 98% of the coins and he gives 1% to each of the lowest ranking pirates and nothing to the other 2 higher ranking pirates, he should hopefully get at least 2 votes and plus himself, meaning he doesn’t get killed.

12. err… 13. geesh

14. the same way everything else in the world doesn’t appear upside down. The eye interprets inverted images the right way up.

15. Something that vibrates and can be worn, like a wrist band or head band, or a watch, or whatever.

16. I’d start a business that sells kiddies entertainment/educational online or software products. People invest in their children. If something is attractive and desirable for children and it’s good and educational for them parents won’t hesitate to buy it for them.

17. Entrepreneurship Awards, with an audience of other Entrepreneurs, Creative Thinkers and Innovators.

18. Check another light switch, if it works there’s a problem with the first light’s light bulb, if not, check the fuse box to see if your anything has tripped. No, Check the fridge, or some other electrical appliance. If they’re working, check the light bulbs, else call a friend and check if their electricity is off. Last resort, phone an electrician.

Miquel, you are so Generation Y. You could check the streetlights or your neighbours’ lights to see if the power is out in your ‘hood.

Doh! forgot the house had windows. I could just if the neighbours lights are off :) duh.

13. Primes are only divisible by 1 and the number itself. Divisible by 6 requires it be divisible by 2 and 3 simultaneously. Every 2nd number is divisible by 2 and every 3rd by 3. In a number sequence with 3 numbers, with 2 of them not divisible by either 2 or 3, it stands to reason that the last will be divisible by both 2 and 3, hence by 6.

Extending the analogy, the 3 number before and 3 number after the sequence will be divisible by either 2 or 3 (not both), ensuring there can never be prime triplets.

Oupoot, you are a genius! Eve, quickly remove that answer less people find it here too easily!

1. How big is the bus?

2. Nothing, I wouldn’t even consider doing it myself, thats madness :)

3.I don’t have an eight year old nephew, and if I did he could probably google the answer anyway.

Skipping now.

8. I would take the wager (*hint no reference is made to who actually pays the money, assuming it’s not you, thats $1 you didn’t have before)

11. Give 100% to the 2nd pirate, your worst threat, if all goes according to plan he will get killed making it a four way split which is far better than before. Besides the ninja’s would most likely beat you too the gold and steal it anyways.

18. Nothing this is South Africa we’re used to being kept in the dark and fed bullshit (mushrooms!)

Seriously now, who are you Oupoot? I believe Google pays a $3000 referral fee for new recruits. I found you first, don’t you forget it!!

The big old elephant in the Knysna forest – if you know your “Kringe in n Bos” :)

Considering the pair primes greater then 6 and the fact that a prime number is only divisible for 1 and the number itself

we conclude that prime numbers must end in 1, 3, 7, 9 because if the number ending in:

0: The number will be divisible at least for 2, 5, 10. So, it will not be prime.

2: The number will be divisible at least for 2. So, it will not be prime.

4: The number will be divisible at least for 2. So, it will not be prime.

5: The number will be divisible at least for 5. So, it will not be prime.

6: The number will be divisible at least for 2. So, it will not be prime.

8: The number will be divisible at least for 2. So, it will not be prime.

This give us the following ranges for possible pair primes.

_1, X, _3 and _7, Y, _9

A number to be divisible for 6 must be divisible for 2 and 3 simultaneously.

It is easy to see that all numbers between pair primes will be divisible for 2.

So, the problem is to prove that the number is divisible for 3 as well.

A number to be divisible for 3 must have the sum of all of its algarisms a multiple of 3.

If we apply this rule recursively we will identify that a number to be divided by three

will have a recursively sum of its algarims equal 3, 6 or 9.

So, if we recursively sum the algarisms of a prime number it will be one of the values: 1, 2, 4, 5, 7 or 8.

Analyzing each possible option and the possible prime ranges we conclude that

The recursively sum of the first prime number in the pair prime can not be 1. Because if the sum of the

first number is 1 the second one should be 3 that would mean that the second number of the prime pair

is not a prime number because it would be divisible for 3.

The recursively sum of the first prime number in the pair prime can not be 4. Because if the sum of the

first number is 4, the recursive sum of the second prime should be 6 this would mean that

the second prime number is divisible by 3

The recursively sum of the first prime number in the pair prime can not be 7. Because if the sum of the

first number is 7, the recursive sum of the second prime number should be 9 this would mean that

the third number is divisible by 3.

With this we reach the necessary conditions to have a prime pair number

condition 1: The prime pair will be in the range:

_1, X, _3 and _7, Y, _9

Condition 2: The recursive sum of the algarisms of the first prime number should be 2, 5 or 8

These two conditions prove that the number between a prime pair will be divisible for 2 and 3 simultaneously.

Because the number will be even (divisible for 2) and the sum of the algarisms will be divisible for 3.

So, being divisible by 6.