In my practicse...i am constantly scoring score of 70%(70% of attempted were correct)..i am not able to pass throught this hurdle..

i am not able to understand whether this scoring rate is good,( i think it can be improved but)..if i start trying to get more scoring rate,the time factor is coming
in to picture.

to get high score..what should be the percentage i can aim for.?
are questions in manhattan are generally tough?

plz guide me

PS: I am doing gmat reading comprehension sample questions(manhattan)