Hello aspirant,

No , Permutations and combinations topic is not included in GATE CSE syllabus. The topics for GATE CSE( Engineering mathematics) are given below :-

Engineering Mathematics

Discrete Mathematics: Propositional and first order logic. Sets, relations, functions, partial orders and lattices. Groups. Graphs: connectivity, matching, coloring. Combinatorics: counting, recurrence relations, generating functions. 
Linear Algebra: Matrices, determinants, system of linear equations, eigenvalues and eigenvectors, LU decomposition.

Calculus: Limits, continuity and differentiability. Maxima and minima. Mean value theorem. Integration.

Probability: Random variables. Uniform, normal, exponential, poisson and binomial distributions. Mean, median, mode and standard deviation. Conditional probability and Bayes theorem.

Hope it helps!!!

yes it is,

Getting through Permutation and combinations can be as hard as you can make it or simple as much as you dedicate your focus.

Understanding it solely depends upon your the area of thinking about the possibility that can arise in a question asked. Basically permutations and combinations are never asked directly in GATE. They are asked with a question of PROBABILITY.

Cracking these three will be a lot easier if you just start from the basics by following the steps mentioned below-:

1. solve the question of probability from the book R.D. SHARMA MATHEMATICS CLASS 10 (for basic understanding of the topic).
2. Then move to R.D. SHARMA class 11 and finally to class 12.
3. You can also use the web which will be huge beneficial , the lectures of sal khan from khan academy. He explained the topics very deeply and with the basic concepts . Guaranteed help.

By the way if you have NCERT , then voila nothing beats NCERT MATHS books.