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Comment by scscsc | Hacker News Reader

' “Say an advertiser makes $0.10 every time someone clicks on their ad. Only 20% of people who visit the site click on their ad. How many people need to visit the site for the advertiser to make $20?” I froze. The problem sounded easy but I didn’t want to cause an awkward silence trying to solve it. '

The problem only sounded easy? Isn't this what you learn in 3rd grade? When you can't do this stuff you shouldn't be allowed near numbers.

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Yeah, it's easy. When you deal with logic problems all day. Or if you're used to solving problems in your head.

Personally, I solved it easily in my head. But, I had to read the problem the first time, then read it again slowly getting all the numbers into the proper places in my head. An interview is a stressful place, so easy things can get a lot harder.

She spent 5 minutes on it, 5 Minutes...

Yeah, I worked it out just as the interviewer explained it. $0.1 per click, 20 out of 100 visitors click, that's 20*0.1=$2.0 per 100 visitors. We need $20 dollars so we need 1000 visitors. This really is child's play. Honestly I think the pressure must have crippled her.

would it have been awkward to write down the equation and then solve it? keeping a legible notebook and writing documentation are even better than doing things in your head and spewing magic numbers. i frequently have reason to do back of the envelope sanity checks...no reason not to use an envelope or a notebook, though.

That might be more obvious to the interviewee if the interview were done in a room with a whiteboard. They could ask to use the whiteboard to sort things out. Over the phone it's possible for people to get the impression that they are supposed to spew and answer right away. It's just a matter of mindset though.

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