You can count on a percentage of exam questions that test your ability to recall formulas from the PMBOK® and use those formulas to solve the problems posed to you in the questions. To answer these questions correctly you have to first identify the need for a formula; if it's a mathematical question it's very likely to require one. Once you've identified the need for a formula you simply have to choose the correct one, plug in the values, and calculate the answer.
Choosing the right formula sounds simple enough in the comfort of your living room or office but you'll need to recall it under pressure, when you're writing your exam. Here are some tips to relieve some of that pressure and improve your performance:
Identify all the formulas that you could be askedto use on the exam. I won't list them all here, but will advise you that if it doesn't appear in the PMBOK® it won't appear on the exam. Start with the obvious ones such as those used in Earned Value Management..
Commit these formulas to memory and practice using them to solve exam type problems in the relevant knowledge areas.
When you enter your examination room and orient yourself, write all the formulas you've memorized onto a sheet of scrap paper that the examiners will provide. You may also want to categorize them, e.g. EVM formulas, etc.
When deciding which formula to use to solve a problem, check to see if all the variables needed to solve the formula have been provided (except the result, of course).