|At a company I interviewed with in the early 90's, when someone came in for an interview, the receptionist handed them a written test. The written test consisted of a single problem:
X^2 + 5X - 14 = 0
Solve for X.
If they could solve that, they got to talk to an engineer. If they couldn't, they were politely shown the door.
Only one person in ten got it.