In a post I read of yours you said that with the exception of 3 things (lines, ……) there are no other formulas you should memorise. In other posts of your I have seen you use the combinations formula. What are your thoughts on using the permutations and combinations formula ?
Could you point me in the direction of any posts you have made (or section in your book) where you discuss counting problems specifically.
You never need permutations or combinations for the SAT. Often, trying to use them will lead to mistakes. My official position is that you don’t need them, which is why I leave them out of my book completely.
You can find some counting posts here: