You have finally landed that big job interview, you are prepped, motivated and perfectly turned out. But do you know how many golf balls you can fit inside the average school bus? Or why manhole covers are round and not square?

You have finally landed that big job interview, you are prepped, motivated and perfectly turned out.

But do you know how many golf balls you can fit inside the average school bus? Or why manhole covers are round and not square?

And could you give the interview panel a good estimate on how much you should charge for cleaning every window in Dublin? Come on! Tick-tock!

It's a jungle out there in the job market and it appears that simply having the right qualifications, skill-set and a go-getting attitude is no longer enough.

The interview process, already one of the most stressful trials of life, is getting even tougher as big companies devise ever more fiendish methods for testing applicants. The latest method used by major tech companies such as Yahoo, Google and Microsoft are so called 'Open-Ended Logic-Problem Screening Tools', or put more simply: 'The manhole question'.

Seemingly random questions such as: "Why are manholes round?" have become commonplace in Silicon Valley in California and are increasingly being taken on in other sectors. Interview panels are not so much interested in the correct answer to a tough question as they are in how a prospective employee might try to solve it.

The technique is in the news at the moment, after a Seattle-based job interview coach called Lewis Lin posted a list of questions on the internet that are regularly fired at job applicants to Google. These included the dreaded 'manhole question' as well as some even more bizarre conundrums featuring pirates, food-blenders and piano tuners.

Microsoft are the people credited with pioneering the method in the mid-'90s when job candidates would be peppered with off-the-wall questions such as: "How much does a 747 weigh?" The interview panel were not so much looking for the right answer in tonnes as how the candidates would react to being presented with a problem that they could never have prepared for.

"We want to gauge people's creativity," says Warren Ashton, recruiting manager at Microsoft.

{module Island Banners|xhtml} The manhole cover problem is Ashton's personal favourite and he says candidates do actually come up with answers. The most common answer, he says, is that a square manhole cover, tipped at an angle, could fall through the hole.

"But some people recognise that you can roll a round manhole cover from site to site. Others figure that you save money by making it round because of tooling requirements. You want to see people taking their conclusions as far as possible."

The questions may seem cruelly obscure but they are more relevant to a job interview for a high-tech company than you might think. "Employers want to see if you can make an estimate in the ballpark, within an order of magnitude," says Mark Jen, a former Google employee. "Employees in high-tech companies are constantly making educated guesses rather than calculating exact answers, so a good interview should probe how well a candidate handles such estimates."

It's why interviewers for internet sales giant Amazon, for example, have been known to ask job candidates to guess how many gas stations there are in the United States or to ballpark the bill for washing all of Seattle's windows. Some software design companies regularly ask job candidates to describe a chicken using a programming language.

The internet auction site eBay often hits candidates with a problem that goes like this: You have five pirates, ranked from 5 to 1 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? (Here's a hint: One pirate ends up with 98pc of the gold.)

Google, who have their European headquarters in Dublin and are recruiting at the moment, are widely recognised as having the most innovative (or offbeat, depending on your point of view) recruitment techniques.

The company once famously reeled in engineers by posting complex maths problems on a billboard along Highway 101 in Silicon Valley in California. Passing motorists were invited to submit their solutions to an undisclosed website. (The site's URL or internet address was hidden in the answer.) If you got to the site, you were asked a second, more difficult question. If you answered that one correctly, you were invited to submit your resume.

It may seem fiendish, it may seem deeply unfair. But the message is clear for job seekers: forget about listing your greatest strengths and weaknesses and start thinking manhole covers.