feedback on your gmat experience

You can read the stickies posted above.

However, I've frequently seen test takers who didn't get more than 3 questions about P&C, many of them got one simple in the first ten. In addition to this, many questions you will find posted here or in the challenge are above the standard level of difficulty, especially in regard to permutations and combinations. So my advice: do learn basic concepts, learn the technique of [total outcomes - unfavorable outcomes]. I have not taken the GMAT, but basically I'm summarizing what I read in the last few months in this section of GmatClub Forum.

Trigonometry is NOT tested. Some people prefer solving geometry questions with some trigonometric concepts. I think this is not advisable if you need to learn additional formulas.