I think it’s a best practice to write out the full formulas and then fill with your variables. Even if you get the question wrong the graders are probably more likely to award you partial credit.
writing the forumula is a huge waste of time, but if you write the correct formula down but get the calculation wrong would you still get partcial credit?
Schweser secret sauce says even if you write a formula that looks mostly correct but has a missed out term or term in the wrong place you will still get some points.