Top companies seem to love tough interview questions.

That's why it's important to be prepared.

Fortunately, there's Glassdoor. The job site hosts reviews and ratings for 640,000 companies in 190 countries.

Glassdoor recently analyzed all of the approved interview questions that US-based job candidates shared on its site during the last 12 months and picked out the ones that had been rated "very difficult" or "difficult" by community members.

Visit Glassdoor for a complete list of tough questions, which appear in no particular order.

Here are some of the potentially pitfall-inducing questions:

1. 'How do you explain a vending machine to someone who hasn't seen or used one before?'

More Bloomberg interview questions »

2. 'How many fire hydrants are there in Los Angeles County?'

3. 'If your current employer had an anniversary party for you, what five words would be written on the cake to describe you?'

Company: Express

4. 'Who in history would you want to go to dinner with and why?'

Company: PSA Airlines

More PSA Airlines interview questions »

5. 'Prove that hoop stress is twice the longitudinal stress in a cylindrical pressure vessel'

Company: SpaceX

6. 'What's the capital of Canada?'

Position: Team leader

Company: OpticsPlanet

More OpticsPlanet interview questions »

7. 'Name a brand that represents you as a person'

Company: Twitter

8. 'Estimate how many employees are in the next building'

8. 'Estimate how many employees are in the next building'
Peter Macdiarmid/Getty Images

Position: Data scientist

More Risk Management Solutions interview questions »

9. 'How many happy birthday posts do you think Facebook gets in one day?'

Company: Facebook

This post originally appeared on Business Insider.