Going for a job interview is nerve-racking at the best of times, but tech giant Google has become notorious for asking fiendishly tough questions.
The company used to ask head-scratching questions such as 'How many piano tuners are there in the world?' and 'How many golf balls does it take to fill a school bus?'.
But some of the riddles were so tough they have now been banned from the interview process.
Recruiter Impact Interview have compiled a list of 140 questions candidates have reported being asked at interviews for various roles at Google, many of which have now been dropped from the process.
One of the tough teasers that candidates used to be asked was: 'How many piano tuners are there in the entire world?'
The riddle is known as a Fermi problem, named after the physicist Enrico Fermi who was known for his ability to make good calculations with very little information or even none.
Its purpose is to test a candidates approximation skills as well as their ability at dimensional analysis.
The puzzle is solved by multiplying a series of estimates to get to the right answer. So a candidate would have to estimate factors such as how many households have a piano, how often they are tuned to figure out how many piano tunings take place a year.
They then need to calculate the average working hours of a piano tuners and the number of jobs they carry out.
The number of piano tunings that take place per year divided by the number per year per piano tuner should yield the answer.
Google candidates going for a role as product manager also used to be asked: 'How many golf balls can fit in a school bus?
To solve it one must calculate the volume of the average golf ball and the the volume of the average school bus, taking into account factors like the seats and other fixtures taking up space.
The answer is the volume of the bus, divided by the volume of the balls.
As well as questions involving calculation and physics, Google used to ask would-be employees to solve logic puzzles.
One of the riddles was: '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?'
Although opinion varies as to the correct answer, a popular solution is to assume that all the cheating husbands will be executed 100 days after the queen's announcement.
Every wife in the village instantly knows when a man other than her husband has cheated, so if there's only one unfaithful man she will know it's her husband and will kill him that day.
Bearing in mind that the queen has said that at least one man has cheated, there could be more than a single adulterer.
If there are two cheaters, 98 women will know who they are. The next day when the wives who have been cheated on see that nobody has been executed they will realise the only explanation is that their husbands are the culprits, and will kill them.
By that logic, 100 cheating husbands will be executed on the 100th day, as the riddle states that every man in the village has cheated on his wife.
A riddle about pirates sounds complicated but the answer is in fact quite simple.
You’re the captain of a pirate ship, and your crew gets to vote on how the gold is divided up.
'If fewer than half of 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?
The solution is to share 51 percent of the treasure.
Another logic puzzled candidates were given to solve was: 'How many times a day do the hands of a clock overlap?'
The hands overlap once an hour, but 11 times in 12 hours and 22 times in a day. This is because the overlap at 12 has already been accounted for.
The overlaps occur at 12, 1.05, 2.11, 3:16, 4:22, 5:27, 6:33, 7:38, 8:44, 9:49 and 10:55 in the morning and after midday at 12, 1.05, 2:11, 3:16, 4:22, 5:27, 6:33, 7:38, 8:44, 9:49 and 10:55.