As the exam is open book, I think a great resource would be “cheat sheets” A5 or A4 pages which outline the basis maths functions and distributions as a sanity check in the heat of the exam. These would also make great flash cards for studying. Would not need to be too complex, simply the formula, name and a few (5?) bullet points about its limitations or uses. Would also help with N,P and other control charts or visual PM tools.