Formulas....do i need to use the formulas used or taught?

I use different versions of the formulas many times (ones more intuitive to me) or i use the PV = PMT = I/Y = N = FV =? in many instances.  But many times there is a formula such as the ones related to tax, related to gifting vs estate etc.  Doing the schweser mock, they give only one guideline answer and it is the exact formula.  Am i judged on the forumlas?  or is having the numbers and answer sufficient?  Any help would be appreciated, just like everything on CFA level 3 there isn't really much guidance and it seems we are supposed to piece everything together on our own.

Thanks