you must I repeat must be good at manipulating formulae.
for example
if Pt=Pd+Ps what does Pd equal?
answer Pd=Pt-Ps
for a multiplication example
if t=d/s
what is distance equal to?
Ans d=s x t
In my atpl (residential) class, there are students of differing academic qualities, from graduates to no formal qualifications. The students weak in mathematics struggled with manipulating formulae and geometrey (working out angles without actually measuring them) however most have managed to plunder on and pass the exams.