Doing that sort of mental arithmetic in a high pressure situation has very little to do with an accounting degree. Yes, it should be easy but I imagine I could make a lot of people flail at questions that they could answer easily sitting around a coffee table.

> Doing that sort of mental arithmetic in a high pressure situation has very little to do with an accounting degree.

Yeah, it does. Accountants work with percentages all the time. And if they can't do literally trivial arithmetic, they aren't fit to be accountants.

He'd give them an hour.

So let's see. What's 10% of $20,000? Then double it? (There are many other shortcuts to the answer.)

Yes. Give someone an hour, of course. I'd expect any minimally educated white collar professional to be able to that without a calculator.

As a verbal problem to answer in ten seconds? I'm more sympathetic with people freezing even if I certainly expect I'd be able to do it absent extreme pressure.

If someone regards an interview question as extreme pressure, I don't know what to say. Except advise the person to do more job interviews until they get used to it.

I sometimes ask people who claim a lot of C experience "could you give me an approximate value for 2^30?", which is vastly more difficult than 20% of $20K for an accountant.

I find it interesting the different approaches that people take. They've ranged from "I know 2^32 is a little over 4B, so 2^30 is a little over 1B", "I know max signed 32-bit int is a little over 2B, so...", "2^10 is a little over 1K, so 2^30 is a little over 1B", to "that's literally impossible and there's no way I could give you so much as an indication as to whether it's positive or negative, even or odd; I'm not even sure it's an integer..."

There are lots and lots and lots of mental shortcuts one can take to get an approximate answer.