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Recent questions and answers in Discrete Mathematics

37 votes
5 answers
1
How many undirected graphs (not necessarily connected) can be constructed out of a given set $V=\{v_1, v_2, \dots v_n\}$ of $n$ vertices? $\frac{n(n-1)} {2}$ $2^n$ $n!$ $2^\frac{n(n-1)} {2} $
answered 16 hours ago in Graph Theory varunrajarathnam 6.2k views
17 votes
5 answers
2
Consider the following well-formed formulae: $\neg \forall x(P(x))$ $\neg \exists x(P(x))$ $\neg \exists x(\neg P(x))$ $\exists x(\neg P(x))$ Which of the above are equivalent? I and III I and IV II and III II and IV
answered 1 day ago in Mathematical Logic Adarsh Pandey 1.8k views
1 vote
4 answers
3
15 votes
4 answers
4
Let $G$ be an arbitrary group. Consider the following relations on $G$: $R_1: \forall a , b \in G, \: a R_1 b \text{ if and only if } \exists g \in G \text{ such that } a = g^{-1}bg$ $R_2: \forall a , b \in G, \: a R_2 b \text{ if and only if } a= b^{-1}$ Which of the above is/are equivalence relation/relations? $R_1$ and $R_2$ $R_1$ only $R_2$ only Neither $R_1$ nor $R_2$
answered 3 days ago in Set Theory & Algebra Amcodes 5.5k views
14 votes
4 answers
5
What is logically equivalent to "If Kareena and Parineeti go to the shopping mall then it is raining": If Kareena and Parineeti do not go to the shopping mall then it is not raining. If Kareena and Parineeti do not go to the shopping mall then it is raining. If it ... go to the shopping mall. If it is not raining then Kareena and Parineeti do not go to the shopping mall. None of the above.
answered 5 days ago in Mathematical Logic iamalokpandey 775 views
31 votes
2 answers
6
A line $L$ in a circuit is said to have a $stuck-at-0$ fault if the line permanently has a logic value $0$. Similarly a line $L$ in a circuit is said to have a $stuck-at-1$ fault if the line permanently has a logic value $1$. A circuit is said to have a multiple $stuck-at$ ... total number of distinct multiple $stuck-at$ faults possible in a circuit with $N$ lines is $3^N$ $3^N - 1$ $2^N - 1$ $2$
answered Oct 17 in Combinatory varunrajarathnam 2.7k views
30 votes
3 answers
7
$n$ couples are invited to a party with the condition that every husband should be accompanied by his wife. However, a wife need not be accompanied by her husband. The number of different gatherings possible at the party is \(^{2n}\mathrm{C}_n\times 2^n\) \(3^n\) \(\frac{(2n)!}{2^n}\) \(^{2n}\mathrm{C}_n\)
answered Oct 16 in Combinatory varunrajarathnam 3.7k views
34 votes
4 answers
8
Let $A$ be a sequence of $8$ distinct integers sorted in ascending order. How many distinct pairs of sequences, $B$ and $C$ are there such that each is sorted in ascending order, $B$ has $5$ and $C$ has $3$ elements, and the result of merging $B$ and $C$ gives $A$ $2$ $30$ $56$ $256$
answered Oct 16 in Combinatory varunrajarathnam 5.2k views
25 votes
5 answers
9
Two girls have picked $10$ roses, $15$ sunflowers and $15$ daffodils. What is the number of ways they can divide the flowers among themselves? $1638$ $2100$ $2640$ None of the above
answered Oct 14 in Combinatory varunrajarathnam 5.6k views
23 votes
5 answers
10
The number of binary strings of $n$ zeros and $k$ ones in which no two ones are adjacent is $^{n-1}C_k$ $^nC_k$ $^nC_{k+1}$ None of the above
answered Oct 14 in Combinatory varunrajarathnam 3.5k views
17 votes
3 answers
11
How many sub strings of different lengths (non-zero) can be formed from a character string of length $n$? $n$ $n^2$ $2^n$ $\frac{n(n+1)}{2}$
answered Oct 14 in Combinatory varunrajarathnam 6.1k views
19 votes
4 answers
12
The number of substrings (of all lengths inclusive) that can be formed from a character string of length $n$ is $n$ $n^2$ $\frac{n(n-1)}{2}$ $\frac{n(n+1)}{2}$
answered Oct 14 in Combinatory varunrajarathnam 3.3k views
4 votes
2 answers
13
A simple graph is one in which there are no self loops and each pair of distinct vertices is connected by at most one edge. Let G be a simple graph on 8 vertices such that there is a vertex of degree 1, a vertex of degree 2, a vertex of degree 3, a vertex of degree 4, a vertex of ... 6 and a vertex of degree 7. Which of the following can be the degree of the last vertex? (A) 3 (B) 0 (C) 5 (D) 4
answered Oct 14 in Graph Theory ayush.5 201 views
17 votes
4 answers
16
How many distinct ways are there to split $50$ identical coins among three people so that each person gets at least $5$ coins? $3^{35}$ $3^{50}-2^{50}$ $\binom{35}{2}$ $\binom{50}{15} \cdot 3^{35}$ $\binom{37}{2}$
answered Oct 13 in Combinatory varunrajarathnam 1.7k views
1 vote
2 answers
18
Consider a graph $G$ with $2^{n}$ vertices where the level of each vertex is a $n$ bit binary string represented as $a_{0},a_{1},a_{2},.............,a_{n-1}$, where each $a_{i}$ is $0$ or $1$ ... $x$ and $y$ denote the degree of a vertex $G$ and number of connected component of $G$ for $n=8.$ The value of $x+10y$ is_____________
answered Oct 13 in Graph Theory arun yadav 287 views
2 votes
2 answers
19
Which of the above lattice is distributve? a) both iii and iv) b) only iv)
answered Oct 12 in Set Theory & Algebra arun yadav 108 views
0 votes
2 answers
20
Answer given is option C , But vertex 10 do not have compliment then how it can be a Boolean algebra ? Also please explain , as no element has compliment greater than 1 , it may or may not be distributive then is there any feasible way to differentiate between option a and d ? Thank you ! P.S : Without using distributive law check, i think its not feasible for more number of vertices.
answered Oct 12 in Set Theory & Algebra arun yadav 222 views
28 votes
7 answers
21
For the composition table of a cyclic group shown below: ... $a,b$ are generators $b,c$ are generators $c,d$ are generators $d,a$ are generators
answered Oct 12 in Set Theory & Algebra Lasani Hussain 3.1k views
1 vote
2 answers
23
2 votes
1 answer
24
Let the number of non-isomorphic groups of order 10 be X and number of non-isomorphic groups of order 24 be Y then the value of X and Y a) 3,2 b)2,7 c)1,7 d)4,5
answered Oct 11 in Mathematical Logic arun yadav 168 views
0 votes
1 answer
25
Consider the following first order logic statement $I)\forall x\forall yP\left ( x,y \right )$ $II)\forall x\exists yP\left ( x,y \right )$ $III)\exists x\exists yP\left ( x,y \right )$ $III)\exists x\forall yP\left ( x,y \right )$ ... $II)$ is true , then $III),IV)$ is true $B)$ If $IV)$ is true , then $II),III)$ is true $C)$ None of these
answered Oct 11 in Mathematical Logic arun yadav 153 views
25 votes
4 answers
26
Provide short answers to the following questions: How many substrings (of all lengths inclusive) can be formed from a character string of length $n$? Assume all characters to be distinct, prove your answer.
answered Oct 8 in Combinatory varunrajarathnam 2k views
0 votes
1 answer
27
The formula for the number of positive integers m which are less than p^k and relatively prime to p^k, where p is a prime number and k is a positive integer is__________- A)p^k(p-1) B)(p^(k-2))(p-1) C)p^k(p-2) D)(p^(k-1))(p-1)
answered Oct 8 in Mathematical Logic Krishnakumar Hatele 53 views
14 votes
2 answers
28
Three candidates, Amar, Birendra and Chanchal stand for the local election. Opinion polls are conducted and show that fraction $a$ of the voters prefer Amar to Birendra, fraction $b$ prefer Birendra to Chanchal and fraction $c$ ... $(a, b, c) = (0.49, 0.49, 0.49);$ None of the above.
answered Oct 4 in Mathematical Logic Amcodes 1.1k views
29 votes
8 answers
29
Let $A$ be a set with $n$ elements. Let $C$ be a collection of distinct subsets of $A$ such that for any two subsets $S_1$ and $S_2$ in $C$, either $S_1 \subset S_2$ or $S_2\subset S_1$. What is the maximum cardinality of C? $n$ $n+1$ $2^{n-1} + 1$ $n!$
answered Oct 4 in Set Theory & Algebra Shashank Rustagi 4.6k views
10 votes
4 answers
30
In a room containing $28$ people, there are $18$ people who speak English, $15$, people who speak Hindi and $22$ people who speak Kannada. $9$ persons speak both English and Hindi, $11$ persons speak both Hindi and Kannada whereas $13$ persons speak both Kannada and English. How many speak all three languages? $9$ $8$ $7$ $6$
answered Oct 3 in Set Theory & Algebra varunrajarathnam 2.5k views
17 votes
7 answers
31
Let $A$ and $B$ be sets and let $A^c$ and $B^c$ denote the complements of the sets $A$ and $B$. The set $(A-B) \cup (B-A) \cup (A \cap B)$ is equal to $A \cup B$ $A^c \cup B^c$ $A \cap B$ $A^c \cap B^c$
answered Oct 3 in Set Theory & Algebra varunrajarathnam 1.7k views
13 votes
4 answers
32
The number of elements in the power set $P(S)$ of the set $S=\{\{\emptyset\}, 1, \{2, 3\}\}$ is: $2$ $4$ $8$ None of the above
answered Oct 3 in Set Theory & Algebra varunrajarathnam 5.2k views
21 votes
3 answers
33
6 votes
3 answers
34
2 votes
1 answer
35
Hello can anyone suggest good video/book to learn generating functions from?..i tried the nptel lecture..it has some audio lag. and i could not make much out of it..I am well versed in combinatorics but my calculus is weak.. Please suggest some resource that teaches generating functions from scratch
answered Sep 28 in Combinatory Himanshu Kumar Gupta 813 views
23 votes
6 answers
37
How many ways are there to assign colours from range $\left\{1,2,\ldots,r\right\}$ to vertices of the following graph so that adjacent vertices receive distinct colours? $r^{4}$ $r^{4} - 4r^{3}$ $r^{4}-5r^{3}+8r^{2}-4r$ $r^{4}-4r^{3}+9r^{2}-3r$ $r^{4}-5r^{3}+10r^{2}-15r$
answered Sep 26 in Graph Theory manish_pal_sunny 1.8k views
25 votes
4 answers
38
28 votes
7 answers
39
Consider the set \(\{a, b, c\}\) with binary operators \(+\) and \(*\) defined as follows: ... $(b * x) + (c * y) = c$ The number of solution(s) (i.e., pair(s) $(x, y)$ that satisfy the equations) is $0$ $1$ $2$ $3$
answered Sep 25 in Set Theory & Algebra mayankso 2.6k views
0 votes
3 answers
40
Which one is the correct translation of the following statement into mathematical logic? “None of my friends are perfect.” $\neg\:\exists\:x(p(x)\land q(x))$ $\exists\:x(\neg\:p(x)\land q(x))$ $\exists\:x(\neg\:p(x)\land\neg\:q(x))$ $\exists\:x(p(x)\land\neg\:q(x))$
answered Sep 22 in Mathematical Logic Dhruvil 184 views
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