'Tell me, why do you really want this job?'

Nervous Businessman in Conference Room
Job interview make you nervous? Glassdoor.com is out with its list of the 25 most difficult companies to interview with and the awkward questions they ask.Fuse / Today

It's your worst nightmare: You're on a job interview, they ask you a question and you don't know the answer. Your heart races. Beads of sweat begin to form. C'mon, don't blow it — THINK!

Since it's better to be prepared for the worst, job site Glassdoor.com is out with their annual list of the Top 25 most difficult companies to interview with.

Consulting firms are notorious for their tough interviews. In fact, they've got a lock on three of the five top spots this year—McKinsey & Co. (No. 1 for a third year in a row), Boston Consulting Group (No. 3) and Bain & Co. (No. 5).

(Read more: The 10 least stressful jobs for 2013)

"The goal of our interview process is to mimic in a controlled setting of what it's like to engage on an actual client engagement," said Keith Bevans, the head of Bain's Global Consultant Recruiting Team. "The goal is to have a business discussion—not administer a quiz or final exam."

There are also a lot of big tech names on the list, including Google (No. 8), Microsoft (No. 16) and Facebook (No. 22). And, some big blue chips such as household-products giant Procter & Gamble (No. 14) and heavy machinery maker Caterpillar (No. 24).

(Read more: Most unfair bosses on TV and film)

A candidate interviewing for a product-manager job at Facebook was asked: "Where do you see the future of Facebook?"

The candidate said after delivering a few ideas, the response from the interviewer was: That's not that different from what we have now. "It was," the candidate said, "but she was apparently expecting more than my already unconventional ideas."

That person did not get the job.

One of the questions asked at an interview for a business-analyst job at Bain was: "Try to estimate the revenue from sale of tickets at Olympics 2012."

*Gulp* How do you answer that?

After you're done swallowing your tongue, the first thing you should remember is: There is no right answer. It's about seeing how you go about solving a problem—a problem you could easily encounter if they hire you.

Often, Bevans said, these "hypothetical questions" are actually based on real issues that came up with clients. In the case of the Olympics question, the company might be looking at investing in a company that does business with the Olympics.

According to Bevans, there are two important things they're looking for in your answer to a question like that: 1) How comfortable you are with numbers and 2) real-world orientation. If you blurt out: "100 million!," that would show a comfort with numbers—but no real-world orientation.

"Wait, you're assuming one in every three people in the country is going to go?!" Bevans said. (The U.S. population is around 313.9 million.)

Here are two possible ways you might approach that question, he said: 1) You might say, "I'll assume X percent of the population in the country tries to make it" then multiply by an estimated ticket price or 2) "I read an article that there are 10 stadiums with an average capacity of 30,000. Assuming the Olympics sell out every day and the games run for 10 days, I'd estimate the revenue at X."

"It's not about the answer—but how you think about structuring it," Bevans said.

Among the other tough interview questions job candidates reported:

"If I took your resume and removed the name at the top, what line on your resume would make your friends read it and recognize you?" - Boston Consulting Group for a consultant job

"How would you build an engine from scratch?" - Rolls-Royce for an engineer job

"How many people watched YouTube in my country in the last hour?"- Google for search-quality analyst job

"What kind of people do you dislike the most?" - Health-care products maker Stryker for a sales rep job

"Teach me something." - Computer-software maker Hubspot for a marketing-consultant job

"Name as many uses for a brick as you can in one minute." – Graphics-chip maker Nvidia for a campaign-manager job

(Read more: Most outrageous interview questions)

The interview process at Bain tends to take a couple of days and generally involves a written component. What that helps with is people who have great analytical skill—but maybe not the most polished, dynamic in-person presentation.

Overall, the companies with the longest interview process were Teach for America, Procter & Gamble and Rolls-Royce, ranging from 46 to 55 days.

The company that had the most negative reviews of the interview process was online-payroll firm Paycom, with 52 percent of job candidates reporting a bad experience. By contrast, the average on Glassdoor for bad experiences is 13 percent.

Rolls-Royce and Avaya had the most positive job-interview experiences reported, with 86 percent of candidates saying they had a good experience. That compares to the average of 52 percent across all companies on Glassdoor.

The companies with the highest employee satisfaction rate were Facebook, computer software firm Guidewire and Bain & Co.

And, while you might think a tough job interview is going to make you sweat bullets, it's important for job candidates to not walk into an interview on the defensive, feeling like they're in front of a firing squad.

"Interviewers always want to see you do well. No one is out to get you! We want to grow as a firm and we need all the qualified people we can get," Bevans said. "We want candidates to walk out of the interview feeling like, 'Wow. I just had a really interesting business discussion.'"

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