How would you build an engine from scratch? Can you estimate the revenue from 2012 Olympic ticket sales? How many people are watching YouTube in a given hour?   


These are just a few of the tough questions job seekers were asked by interviewers in the past year, according to a report released today by, CNNMoney reported.


Using rankings and reviews of interviews posted by thousands of users over the past 12 months, the career website listed the 25 companies that put job candidates through the most rigorous hiring process.


Though the average job seeker faces a 16-day interview process, candidates for most of the companies on the list reported interview times that spanned weeks or even months, according to Glassdoor.


McKinsey & Co., a management consulting firm that advises many of the world's largest companies, was the toughest interviewer for the third year in a row, according to Glassdoor. Candidates reported up to nine rounds of interviews, with tests ranging from case studies to a mathematics exam that one candidate compared to the dreaded GMAT.


"The process itself was grueling - training for case studies in parallel to a full-time executive job is not easy - but also very motivating," one candidate wrote on Glassdoor. To read more, including the list of the 25 toughest torture chambers, make that companies, click here.