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GATE Engineering Mathematics: Discrete Mathematics: Combinatorics (Counting, Recurrence Relations, Generating Functions) – Previous Year Questions

15 GATE previous year questions on Discrete Mathematics: Combinatorics (Counting, Recurrence Relations, Generating Functions) (Engineering Mathematics, Computer Science) with answers and explanations, from every paper.

  1. GATE 2017 CS Q57 (2 marks, Numerical answer) – The number of integers between 1 and 500 (both inclusive) that are divisible by 3 or 5 or 7 is .
  2. GATE 2016 CS Q12 (1 mark, Multiple choice) – Let a n be the number of n-bit strings that do NOT contain two consecutive 1s. Which one of the following is the recurrence relation for a n?
  3. GATE 2016 CS Q36 (2 marks, Numerical answer) – The coefficient of x12 in (x3 + x4 + x5 + x6 + )3 is .
  4. GATE 2016 CS Q37 (2 marks, Numerical answer) – Consider the recurrence relation a 1 = 8, a n = 6n2 + 2n + a n-1. Let a 99 = K 104. The value of K is .
  5. GATE 2015 CS Q45 (2 marks, Multiple choice) – Let a n represent the number of bit strings of length n containing two consecutive 1s. What is the recurrence relation for a n?
  6. GATE 2018 CS Q11 (1 mark, Multiple choice) – Which one of the following is a closed form expression for the generating function of the sequence \a n\, where a n=2n+3 for all n=0,1,2,?
  7. GATE 2019 CS Q15 (1 mark, Multiple choice) – Let U=\1,2,,n\. Let A=\(x,X) x X,\ X U\. Consider the following two statements on A . I. A =n2n-1 II. A = k=1nk nk Which of the above statements…
  8. GATE 2026 CS (CS1) Q57 (2 marks, Numerical answer) – Let G be an undirected graph, which is a path on 8 vertices. The number of matchings in G is . (answer in integer)
  9. GATE 2025 CS (CS1) Q30 (1 mark, Numerical answer) – Let S be the set of all ternary strings defined over the alphabet \a,b,c\. Consider all strings in S that contain at least one occurrence of two…
  10. GATE 2023 CS Q15 (1 mark, Multiple choice) – The Lucas sequence L n is defined by the recurrence relation: L n = L n-1 + L n-2, for n 3, with L 1 = 1 and L 2 = 3. Which one of the options given…
  11. GATE 2023 CS Q48 (2 marks, Multiple choice) – Let U = \1, 2, , n\, where n is a large positive integer greater than 1000. Let k be a positive integer less than n. Let A, B be subsets of U with A =…
  12. GATE 2022 CS Q32 (1 mark, Numerical answer) – The number of arrangements of six identical balls in three identical bins is .
  13. GATE 2022 CS Q36 (2 marks, Multiple choice) – Which one of the following is the closed form for the generating function of the sequence \a n\ n0 defined below? a n=casesn+1, & n is odd\\ 1, &…
  14. GATE 2021 CS Q29 (1 mark, Numerical answer) – There are 6 jobs with distinct difficulty levels, and 3 computers with distinct processing speeds. Each job is assigned to a computer such that: - The…
  15. GATE 2020 CS Q52 (2 marks, Numerical answer) – The number of permutations of the characters in LILAC so that no character appears in its original position, if the two L's are indistinguishable, is…