When you don’t pass the first round, instead of rejecting you outright, they ask you to complete a research task. After you finish it, they reject you anyway and provide no feedback. These are pretty shady companies, yet they claim to be "transparent."

Probability and Statistics Questionnaire that was broken up into 6 easy statistics problems and 6 medium/hard questions. Ended up with a 7/12 and didn't get past first round but it is definitely doable

The first round includes two tasks: a probability exam and a programming exam. The probability exam consisted of 20 questions at the university level, and you had to type in the correct answer. The second task was a programming challenge involving people rotating and throwing balls to the nearest person. The code was not reviewed by a human; instead, it was automatically checked to determine whether the output was correct.