i worked out only official guide 13th edition , when i attempted gmatprep i got a score of 610. I feel i need more exposure to difficulty question both in Q&V. Even though i managed difficult questions reasonably in gmatprep, which i did not expect. If i choose the right materials which can expose me to difficult questions i am confident i can score better. I feel i need to improve in quant topics inequalities,permutation&combination & probability. and in verbal difficult RC'S.please suggest me materials i have 30 days to work on.