It wasn't impossible to answer, it was just a puzzle. It required you to realize some specific property of the problem, or be stuck implementing a suboptimal solution in a fiddly editor with no debugging features.

It also had pretty much zero overlap with actual software development (e.g. it completely ignored actual business needs, which is a big part of what devs should care about).

They give you two or three tests from Codility. You can prepare for them, too: https://codility.com/programmers/

It's actually quite fun to do. I succeeded only one of the three within the time limit, and sent the results of the second one an hour or two later. I still got denied, but was told I could reapply in a couple of months.

The thing is, I'm earning a nice 70 euros per hour with local work. They don't advertise the rates, but I've heard and read it's 20-30% lower than that.