Optiver's mental math consists of 80 questions, although nobody knows the exact score you have to pass, generally people who go into next rounds get to question 65-70, which implies score around 50+. The test (last time I took it in 2018) is actually a multiple choice test, therefore should be a bit easier than what you see here. However the equations at this point are rather more difficult than the actual Optiver test.
Number of Equations
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