How was the difficulty of the UPSC 2020 mains paper? Has anyone finished solving the entire paper?

I have solved to some extent, but don't know the difficulty level of certain topics which I have not finished revising and hence do not remember the formulas and associated concepts.

Among the topics that I have finished revising, I found one problem from numerical analysis section difficult, (the one which has three point lagrange interpolating polynomial and limit for expression of derivative). The rest looked doable/calculation based and I have solved most of them. Apart from that, from the topics that I have not revised yet, modern algebra looks quite easy/ straightforward theory (I studied Algebra in college as I am a math graduate)

Specifically, I have not finished revising PDE, complex analysis, modern algebra, dynamics/statics and mechanics. (I do not intend to study fluid dynamics and will leave it) How was the difficulty level of the paper in these topics? Were the problems mechanical/ from IMS notes or did they require innovation/tricks outside the book?

However, I find that the time for revision is a bit less as the prelims exam was held late this year and also there is only about 2.5 months between pre and mains. I have completed only 7/13 topics, and it is February already. I plan to start prelims specific preparation from 1 Feb onwards. Also, I have not done mains answer writing or ethics or essay preparation. Given my scenario, what do you feel should be the way forward for me?

I am contemplating one of 3 paths currently -

1. Drop CSE ambition for this year and prepare for CSE 2022, by focusing on completing math

and mains specific preparation for now instead of pre .

2. Try to give some time (say 1 hour) daily, even during prelims preparation.

3. Try to take out 1/2 to 1 month out of intensive pre preparation and devote the time to finish math/answer writing.

Any help will be greatly appreciated.

**@AlexanderSupertramp**Thanks a lot. I'll check it out. Do you have math optional too?

**@Celeborn**No, I graduated from IIT Delhi, Mathematics and Computation Department (2019 Batch).

Thank you for taking the time out to answer my question. I will follow this strategy.

**@Davidjones**Thank you for answering my question. I did not solve the entire paper properly, as I have not finished revising all the topics, but I found the questions doable in the papers. As I said, I have completed the syllabus once and faintly remember some topics like Algebra, Complex Analysis and Mechanics/Statics/Dynamics.

However, I have not solved all the questions till the final answer. Could you please point out which questions from the paper were difficult/ what topics had out of the box questions? It will help me to save some time, so that I can try specifically those questions.

Though the Lagrange interpolating polynomial question 8(b) does look difficult. I couldn't solve this in my first attempt. Also, the question contains Fluid dynamics (Q8c), so I wouldn't have attempted it anyway.

The question about lagrange ho jaata bhai if thoda time leke sochte tum. FD ka question was easy ek baar attempt karte tum kyuki difgerntiate karne ke baad easy 0 nikal jaata and y component bhi easily aa jaata. Moment of inertia ka question was real time consumer aur last me answer nahi aaya. Similarly i attempted simplex ka question udher i think meri calculation mistakes hui hai. Bhai i feel second paper mera acha gaya compare kare to. First paper sab easy bol rahe hai but i ll be frank, meri bhut galti hui hai. Hindsight me even i feel paper was easy par i lost time in some questions and baaki questions jaldi me attempt hue. Bhai solve the complete paper with 3 hours deadline. Also kuc environmrnt bana do tab do exam. You will gwt a good idea

Nahin, I have not covered FD (and don't plan to cover it in future also), thats why I said I would leave it.

So, I understand from your comment that time management is important during paper. Hence, practice seems necessary for math paper also. I will give previous year paper (2019 or 2018) like mock test in constrained time now, because I have already seen many questions of 2020 paper and even solved some of them completely, that I thought looked unusual. So, perhaps, if I give the paper, it will not be a good indicator of how well I can write a fresh paper in constrained time. By the way, do you recommend solving test series like IMS, Dias or Shankar, before the actual paper? I was thinking of just solving previous year papers in constrained time like mock test.

Thanks a lot for the advice. Its pretty useful.