You can select 1 chapter as optional only when other chapters are going to be properly prepared. Also please refer & prepare all the sums from PM,SAs & RTPs of last 6 examinations i.e. 3 yrs. If possible also prepare sums frm chapter you hav selected as optional from SAs. In OR try to understand the techniques and try to cover chapters sums from which are of a particular format like Transportation, simplex method , also learn how to draw network. However as transportation & PERT have already been included in May 13 examination there are high chances that they wont be there in Nov 13 but this cant be said 4 sure as standard costing was there in both Nov 12 & May 13. Key is not to afraid & worry. Just think that you are getting your knowledge evaluated & when you wil cross a level you wil 4 sure pass the examination. Please dont take ISCA as a light subject. Only easure some minimum addition to your knowledge base daily and stick to the institute's material. All is & wil be well.