There're a couple parts to your comment. Yes, some third graders could do that no problem, even under the time constraints and pressure. I certainly could - I think I could actually have done it faster in 3rd grade than I could now. It's just like a math test or math competition, and good students have no trouble getting perfect scores on a math test even under intense time constraints (< 1 min/problem) and intense pressure ("If you don't ace this quiz, you'll never get into Harvard and then your life will be wasted.")
The second point of your comment is legit - this sort of time/pressure constraint isn't really representative of the workplace as a whole. Nobody should have someone hanging over them making sure you do your math right in under one minute - you certainly don't at Google. The interviewer probably should've tried to make the candidate feel a bit more at-ease.
But the sort of quick estimation skill necessary for these interview questions is really important. There've been countless meetings when someone (often me) has proposed a solution and I've done some quick mental math calculations only to find out that it just won't work. It's really valuable to get those calculations done in a minute so that you can brainstorm new ideas, rather than waiting until after the meeting when you probably just won't do the math at all.
And this is something that I really wish schools taught more of. Being able to get a quick, mostly-right-but-slightly-wrong answer, and being able to tell what ways your answer is wrong, is probably more important than being able to come up with exact answers or parrot back the formulas you supposedly memorize.
That and how to work with people to get to the answer.
I would want to work out that problem with someone. For that math problem right:
lets ignore the 20 people problem (aka 20%) right now and pretend that all the people who visisted clicked. for every 100 people who visit, they now get 1 dollar (it was ten cents) before). in order to get $20 if a hundred people visited for every dollar, you would need
20,000 people.
One problem, they need to click. and only 20 people click per 100 people. so in order to really make that money, you would have to multiply again by 20. I would take the 2s out and start counting 0s because I would get confused at this point.
400,000 people. I think. I may have screwed up the 0s. But If I didn't have a chance to slow down and write down the problem I think I would have screwed that up badly. I'm not sitting around and doing those math problems all the time...
The second point of your comment is legit - this sort of time/pressure constraint isn't really representative of the workplace as a whole. Nobody should have someone hanging over them making sure you do your math right in under one minute - you certainly don't at Google. The interviewer probably should've tried to make the candidate feel a bit more at-ease.
But the sort of quick estimation skill necessary for these interview questions is really important. There've been countless meetings when someone (often me) has proposed a solution and I've done some quick mental math calculations only to find out that it just won't work. It's really valuable to get those calculations done in a minute so that you can brainstorm new ideas, rather than waiting until after the meeting when you probably just won't do the math at all.
And this is something that I really wish schools taught more of. Being able to get a quick, mostly-right-but-slightly-wrong answer, and being able to tell what ways your answer is wrong, is probably more important than being able to come up with exact answers or parrot back the formulas you supposedly memorize.