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Syllabus: Combinatorics: Counting, Recurrence relations, Generating functions.

$$\scriptsize{\overset{{\large{\textbf{Mark Distribution in Previous GATE}}}}{\begin{array}{|c|c|c|c|c|c|c|c|}\hline
\textbf{Year}& \textbf{2024-1} & \textbf{2024-2} & \textbf{2023} & \textbf{2022} & \textbf{2021-1}&\textbf{2021-2}&\textbf{Minimum}&\textbf{Average}&\textbf{Maximum}
\\\hline\textbf{1 Mark Count} &0&0&1& 1&1&0&0&0.5&1
\\\hline\textbf{2 Marks Count} &0&0&1& 2 &0&1&0&0.67&2
\\\hline\textbf{Total Marks} & 0&0&3&5 &1&2&0&1.83&5\\\hline
\end{array}}}$$

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Highest voted questions in Combinatory

17 votes
2 answers
61
Generalized permutation and combination
How many positive integers less than 1,000,000 have the sum of their digits equal to 19? (using generating function)
How many positive integers less than 1,000,000 have the sum of their digits equal to 19? (using generating function)
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17 votes
8 answers
63
GATE CSE 2008 | Question: 24
Let $P =\sum \limits_ {i\;\text{odd}}^{1\le i \le 2k} i$ and $Q = \sum\limits_{i\;\text{even}}^{1 \le i \le 2k} i$, where $k$ is a positive integer. Then $P = Q - k$ $P = Q + k$ $P = Q$ $P = Q + 2k$
Let $P =\sum \limits_ {i\;\text{odd}}^{1\le i \le 2k} i$ and $Q = \sum\limits_{i\;\text{even}}^{1 \le i \le 2k} i$, where $k$ is a positive integer. Then$P = Q - k$$P = Q...
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16 votes
6 answers
64
TIFR CSE 2018 | Part A | Question: 6
What is the minimum number of students needed in a class to guarantee that there are at least $6$ students whose birthdays fall in the same month ? $6$ $23$ $61$ $72$ $91$
What is the minimum number of students needed in a class to guarantee that there are at least $6$ students whose birthdays fall in the same month ?$6$$23$$61$$72$$91$
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15 votes
2 answers
67
TIFR CSE 2017 | Part A | Question: 6
How many distinct words can be formed by permuting the letters of the word $\text{ABRACADABRA}?$ $\frac{11!}{5! \: 2! \: 2!}$ $\frac{11!}{5! \: 4! }$ $11! \: 5! \: 2! \: 2!\:$ $11! \: 5! \: 4!$ $11! $
How many distinct words can be formed by permuting the letters of the word $\text{ABRACADABRA}?$$\frac{11!}{5! \: 2! \: 2!}$$\frac{11!}{5! \: 4! }$$11! \: 5! \: 2! \: 2!\...
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14 votes
5 answers
70
ISI 2004 MIII
The number of permutation of $\{1,2,3,4,5\}$ that keep at least one integer fixed is. $81$ $76$ $120$ $60$
The number of permutation of $\{1,2,3,4,5\}$ that keep at least one integer fixed is.$81$$76$$120$$60$
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13 votes
2 answers
73
TIFR CSE 2011 | Part A | Question: 2
In how many ways can the letters of the word $\text{ABACUS}$ be rearranged such that the vowels always appear together? $\dfrac{(6+3)!}{2!}$ $\dfrac{6!}{2!}$ $\dfrac{3!3!}{2!}$ $\dfrac{4!3!}{2!}$ None of the above
In how many ways can the letters of the word $\text{ABACUS}$ be rearranged such that the vowels always appear together?$\dfrac{(6+3)!}{2!}$ $\dfrac{6!}{2!}$ $\dfrac{3!3!}...
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12 votes
2 answers
74
GATE CSE 1990 | Question: 3-ix
The number of ways in which $5\; A's, 5\; B's$ and $5\; C's$ can be arranged in a row is: $15!/(5!)^{3}$ $15!$ $\left(\frac{15}{5}\right)$ $15!(5!3!)$.
The number of ways in which $5\; A's, 5\; B's$ and $5\; C's$ can be arranged in a row is:$15!/(5!)^{3}$$15!$$\left(\frac{15}{5}\right)$$15!(5!3!)$.
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10 votes
1 answer
75
Discrete mathematics - Combinatorics
An integer is called snakelike if its decimal representation $a_1a_2a_3...a_n$ satisfies $a_i < a_{i+1} $ if $i$ is odd and $a_i > a_{i+1}$ if $i$ is even. How many snakelike integers between $1000$ and $9999$ have four distinct digits?
An integer is called snakelike if its decimal representation $a_1a_2a_3...a_n$ satisfies $a_i < a_{i+1} $ if $i$ is odd and $a_i a_{i+1}$ if $i$ is even. How many snak...
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10 votes
2 answers
76
GATE1991-01,xiii
The number of integer-triples $(i,j,k)$ with $1 \leq i,j,k \leq 300$ such that $i+j+k$ is divisible by 3 is________
The number of integer-triples $(i,j,k)$ with $1 \leq i,j,k \leq 300$ such that $i+j+k$ is divisible by 3 is________
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9 votes
9 answers
78
Kenneth Rosen Edition 6 Question 45 (Page No. 346)
How many bit strings of length eight contain either three consecutive 0s or four consecutive 1s?
How many bit strings of length eight contain either three consecutive 0s or four consecutive 1s?
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