how to remember the formation of various equations in arithmetic ?

First of all, I don't know how many people would agree with me, but I feel in arithmetic equations should be last resort. All exams have options(Few questions in CAT does not, so for that you need to be clear with your concepts. Pay attention, I said concepts, not equations). Talking with reference to CAT, mostly arithmetic questions are logical and options make them even easier. So, rather than remembering equations, you should learn were to use equations and where not to. If you are confused, post some question so that I could explain my thought process for solving arithmetic questions.