It is enough to surely get 30-50 marks but that won’t get you even to an NIT unless you have some reservation. If you carefully read the below points you can get higher marks.
How to solve?
Getting answer to the previous year GATE questions takes you nowhere as in GATE questions RARELY do get repeated. But in many topics, same type of questions get asked. One example is cache memory from CO & Computer Architecture subject. If you know properly to solve one question from this topics, you can solve many similar ones. And if you are seeing someone’s solution, make that your own by really understanding each and every step. You should never byheart someone’s solution as in most times they will just backfire in GATE.
So, if you are solving a previous paper and if you don’t know an answer, first look in a standard resource (either standard text book or resource given by some top university) and understand the topic. If you still can’t get an answer show your solution to someone and understand where you went wrong. Only if it is unavoidable check someone else’s solution. Also realize that the first few problems of a subject should take a LOT LOT more time to solve than the rest because those should be cementing your concepts as well.
I know to solve all previous year GATE questions. Will I get into top 100?
If you really know the proper way to solve the previous GATE questions you have a high chance of getting into top 100. You should be able to get at least 80 marks from them and usually 60+ is enough for a good rank (if exam is easy this can go up to 70+ as happened in 2011). But this means you shouldn’t make any mistakes while reading the questions and interpret all questions properly- no space for silly mistakes. To get into the safe space of 90+ you have to understand the topics properly. One example is Database Normalization. If you know how to identify the keys from Functional Dependencies and able to identify the Normalization level, you can answer most (almost 90%) of the questions from this area. But to guarantee 100%, you need to understand what is normalization and why is it done, what is the significance of Functional dependencies etc.
Understand the concepts- what does this mean?
One example is “what is the complexity of merge sort?”. If you know it is O(nlogn)O(nlogn) then it is not enough for GATE. You must know how that O(nlogn)O(nlogn) is the TIGHTEST upper bound for the complexity of merge sort and HOW that came. In short those making GATE questions know that people will be by hearting these complexities and they will make sure the question is twisted and only those who know how to derive the complexity can answer that.
Can I understand all concepts?
Probably no. But do as much as you can and especially do understand the concepts in Algorithms and Data structures- they are the subjects where the questions are usually twisted. I have seen many people leaving Theory of Computation for preparation. But that is not a good idea. Usually questions from TOC are asked quite a bit for GATE. And these questions are easily answerable if you have studied till Turing machines and reduction. Practise do help in TOC as questions come only from a small class of problems.
How many papers should I solve?
There are people who got top 100 even without solving a single previous year paper. So, even 1 is enough. For those who have good grip in the subjects, solving three papers of GATE 2014 is enough. If you have time you can solve papers from 2010 on wards. Only for those who prepare solely from previous GATE papers, I encourage to solve papers before 2010. And I have found that many questions from 1991-1998 to be bit tough. And many of the topics asked then are not in syllabus now. So, please be aware of these while solving those papers.