Here’s a tricky one, Google

If you also know, say, how to get four people across a rickety bridge under difficult circumstances at night — flashlight that will last only 17 minutes, bridge can’t hold more than two people, one of the party takes half an hour to cross but needs to go to the lavatory halfway, the usual stuff — then all the better.

These days interviews are rigorous, and if you’re trying to get a job with Google they don’t come much tougher. The company, which employs about 20,000 people worldwide, gets 3,000 job applications a day. Just to give you some idea of the competition for jobs, there were only 50 UK vacancies being advertised last week.

An extensive list of Google questions was posted last month on a blog written by Lewis Lin, a recruitment consultant in Seattle who has helped young graduates to find jobs with both Google and Microsoft. Many are software and engineering problems that you might expect to be asked at an interview for a big computer firm. But you can also expect to be asked about those pirates, 100 adulterous husbands, manhole covers and all the dirty windows in Seattle.

How times have changed. It’s not that long ago — probably about 20-30 years — when job interviews at big companies went something like this:

Interviewer: “Didn’t your father used to work here?”

Interviewee: “Yes. He sends his best wishes.”

Interviewer: “Do you still play rugby, by the way?”

Interviewee: “Yes.”

Interviewer: “Jolly good. When can you start?”

This was the way young people got jobs pretty much everywhere. Not any more.

According to computer geek legend, it was Microsoft that first started using puzzles in formal job interviews, largely because Bill Gates enjoyed puzzles more than he enjoyed interviewing. But such questions will be familiar to university applicants, who’ve had to put up with this sort of thing for years.

A book called So You Want to Go to Oxbridge? Tell Me About a Banana lists the sort of questions that Oxford and Cambridge applicants have faced in recent years. “If ancient history has a shape, what shape might that be?” is one of them. “What is the most interesting thing about a squirrel?” is another (to which the answer is, duh, obviously: “red squirrel or grey squirrel?”).

“Microsoft and Google are known as the two companies that have historically used brain teasers in the interview process,” says Lin. “Candidates usually react in one of two ways. Some dismiss puzzle or estimation questions as ridiculous; others clam up under the stress of an unfamiliar question. As far-fetched as the question may sound, do take it seriously. Take a deep breath, give it your best shot.”

Some questions don’t actually have an answer. The interviewer is looking for an analytical approach rather than a correct solution. And even if you get the job, you won’t necessarily discover the right answer to the questions.

“Many of us here are still trying to figure out how many tennis balls can fit into a small room, or the number of people currently travelling by air in the world,” says Laura Scott, Google’s UK spokeswoman.

“Googlers love creative ideas, finding innovative solutions and cracking complex problems — it’s what keeps us on our toes. That’s why we aim to ask many different and engaging questions in interviews.

“The questions give us a sense of how someone works through a difficult problem, which in turn helps us get to know a person and see whether they would be a good fit for Google.”

Sometimes — just sometimes — interview questions are easier than they seem. When Professor Marcus du Sautoy was interviewed to read maths at Oxford, he was asked whether he could change a light bulb. “I thought I was meant to come up with a witty joke,” says du Sautoy, now Oxford’s professor for the public understanding of science. Actually, the tutor just wanted some help to change his light bulb.

Figure these out

Are you the right stuff for Google? Here are nine typical questions asked at Google interviews. Answers have been supplied by Marcus du Sautoy, Oxford University professor for the public understanding of science; Alexander Paseau, philosophy fellow at Wadham College, Oxford; David Wallace, philosophy of physics fellow at Balliol College, Oxford; Roland White, professor for the private misunderstanding of science at the University of Wapping.

1 You have eight balls all of the same size. Seven of them weigh the same. One of them weighs slightly more. How can you find the heavier ball by using a balance and only two weighings?

2 You’re a pirate ship captain, and your crew gets to vote on how the gold is divided. If fewer than half the pirates agree with you, you die. How do you recommend apportioning the gold in such a way that you get a good share of the booty, but still survive?

3 Every man in a village of 100 married couples has cheated on his wife. Every wife in the village instantly knows when a man other than her husband has cheated, but does not know when her own husband has. The village has a law that does not allow for adultery. Any wife who can prove that her husband is unfaithful must kill him that very day. The women of the village would never disobey this law. One day, the queen of the village visits and announces that at least one husband has been unfaithful. What happens?

4 How many golf balls can fit in a school bus?

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

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

7 How many piano tuners are there in the world?

8 Why are manhole covers round?

9 A man pushed his car to the hotel and lost his fortune. What happened?

Answers are below

Answers 1 Weigh balls 1, 2, 3 against 4, 5, 6. If they balance, compare 7 and 8; if they differ, take the heavier set (say 1,2,3) and weigh 1 and 2. If they balance, ball 3 is heaviest.

2 If there are N pirates, give half of them just over 1/N of the loot each (which is more than they’d expect by even distribution). Keep the remaining loot (just under half the total).

3 Suppose there are only two married couples in the village. When the queen makes her announcement, Wife 1 knows Husband 2 was unfaithful. Now she knows that if Wife 2 sees that Husband 1 is faithful then Wife 2 will kill Husband 2 on the first day because at least one of the two men is unfaithful and it isn’t Husband 1. However, Wife 2 doesn’t kill her husband. The only reason being because she knows Husband 1 is unfaithful. Because both husbands are still alive on the second day the wives know both are unfaithful. So on the second day both husbands are killed by their wives. What happens with 100 married couples is that the wives have to wait till the 100th day before they can prove that their husband is cheating. On the 100th day there is a bloodbath: all the men are killed by their wives.

4 Full marks for mentioning the Kepler conjecture on packing spheres into a three-dimensional space. The fraction of the volume you can fill is /(3 2). “This comes out at roughly 74%”, says Professor du Sautoy.

5 We got a quote: Valhalla window cleaning service of Seattle says it will do all the residential windows for $90m and all the commercial ones for $100m. Valhalla usually charges $125 for a “normal” 18-window house.

6 22 7 The UK’s Pianoforte Tuners’ Association has 200 members, but vice-president John Lambert thinks there are about 1,000 people tuning British pianos. Let’s say the UK population is 60m. That’s one tuner per 60,000 of the population. Let’s then make the assumption that everybody in the world — approx 6.7 billion — is as keen on playing the piano as the British (and yes, it’s a rather unlikely assumption). That means there are 111,667 piano tuners in the world. But Dr Wallace puts the figure at 10,000. “There aren’t many outside the West’s 600m population,” he says. “The average town has maybe two or three but is servicing a wider area with maybe another 50,000 people. So, vaguely, one per 50,000. Or about 10,000.”

8 They’re not always round, but you can’t drop a round cover down the hole like you can with a square cover (which can fall down the diagonal). “The shape of a 50p coin will also work,” says Professor du Sautoy.

9 He was playing Monopoly.

Additonal reporting Josh Glancy