Dear,
If you have an approach to just attempt the exam without planning how to succeed then the chances of failure will be high. One cannot pass CA exam by luck all the time. One need hard work. You cannot afford to attempt only 80 % of the questions and hope for clearing. You have to attend 100% you need to fix time to spend on a question in relation to the marks awarded to it. if the method adopted by you do not give desired result change your method. Actually I am a 52 year old CA passed out in 1992. Not in academics.So am not very much sure on the books what you should be referring. All I am saying is if the preparation is not good due to time constraint you may postpone appearing for the exam and prepare well. Appear once you have done enough preparation. First of all don't approch the exam only with the intention to clear spend quality time in clearing the concept of each and evetry subject.. Analyse. The subjects costing, IDT and DT highly relies on Logic if your logic is clear on any subject you can approach the question more analytically and your answer will be near to correctness.
All the best
VVS