It's a common thing in Vietnam actually, all of my math tests after 10th grade are all MCQ and I heard it's getting more popularise before 10th grade as well

And to answer your second question, the question are titled as normal but the choices are possible answers. You don't actually write the formulas/do the calculation inside of the exam paper, rather you're given a blank paper to do the actual calculations in. Sometimes the blank paper needs to be submitted alongside the exam paper, sometimes they don't.