I gave the paper last year. Maths was just too easy. I finished in some 15-20 mins. Economics I cracked 4 questions and wrote semi-right answers on the paper. As per previous trends, I think we needed to nail at-least 5-6 questions if the paper is tough and try to nail all Qs if we need to get a call for the top 60 for a surety.
ISI has been getting a lot of attention for a place of quality education. And this might have caused them to up the level of papers to filter even better quality candidates. Saying that, my speculation is that we may see more number of questions.
For the same, I have practiced a lot of questions and read only basics of theory. I think one should practice a full array and types of questions to score well. I am currently revising math problems.
I am expecting more questions to come up as we reach May 10. Best approach for anyone would be to solve as many questions as possible.
Regards
Yoda
seize the day we must!
Win We Must