Recent questions and answers in Combinatory - GATE CSE Doubts

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Collinear points on a plane
Suppose 10 points are drawn on a plane such that exactly 4 of the points are collinear and among the remaining points no three points are collinear. How many distinct lines can be drawn by connecting any two among these 10 points?

asked 9 hours ago in Combinatory by Akash Papnai (16 points) | 5 views

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MADE EASY CBT-2
The number of nine digits numbers which can be formed using this digits 0,0,0,1,1,1,2,2,2 such that no two pairs of same type of digits are together? ( eg. 00 or 11 can not be together).

asked 1 day ago in Combinatory by Naeem Khan (6 points) | 8 views

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GATE MOCK TEST 3 GATE 2019 Q60 Combinatorics
I tried like this: Required probability= ways to put 3balls in box 1 / total ways to put 12 balls in 3 box = number of solutions to x1+x2=9 / number of solutions to x1+x2+x3=12 Will it not worth with star and bar method?

answered 2 days ago in Combinatory by neeraj_bhatt (237 points) | 14 views

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Made Easy CBT-1
1) The Number of Solution set(x,y) for the equation 4x+7y=3, such that -99<=x<=99 and -100<=y<=100, where x,y belongs to Integers. 14 b. 29 c. 15 d. 30

asked 2 days ago in Combinatory by Dheeraj Varma (8 points) | 20 views

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MADE EASY FULL TEST 7 advance level
the number of even palindromes over the alphabet {p,q,r} upto length n equals 121? what is n? I calculated for 0,2,4,6,8 and individual comes out to be 1,3,9,18,69 and it adds upto 100, so how answer can be 8?(they have given 8 as answer) what is the mistake?

asked 3 days ago in Combinatory by Rajat Maheshwari (10 points) | 18 views

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Ace full length : Discrete Maths

answered Jan 10 in Combinatory by Pratyush Priyam Kuan (774 points) | 35 views

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Made easy test series: Combinatorics
The number of ways can 5 letter be put into 3 letter boxes A, B, C if letter box A must contain atleast 2 letters ________. Can anyone give good explaination with answer for above question.

asked Dec 31, 2019 in Combinatory by vishal burnwal (119 points) | 19 views

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MadeEasy Demo Test Q30

asked Dec 30, 2019 in Combinatory by ssap09 (42 points) | 6 views

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Made Easy FULL LENGTH-1
The number of 3 letter words possible for the word “ESSEL” is equal to __________

asked Dec 30, 2019 in Combinatory by Dipanshu Rana (34 points) | 12 views

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1 answer

Ace academy volume 1, page number 73, question number 68.

answered Dec 24, 2019 in Combinatory by neeraj_bhatt (237 points) | 26 views

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ACE full length mock test
Eight people enter an elevator at the first floor. The elevator discharges passengers on each successive floor until it empties on the fifth floor. Number of different ways this can happen______? Answer given 40824

answered Dec 19, 2019 in Combinatory by Mk Utkarsh (472 points) | 32 views

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#combinotrics
Q.the number of way six distinct balls be distributed into 3 distinct urns.If each urn contain at least one ball are....

asked Dec 7, 2019 in Combinatory by amit166 (138 points) | 7 views

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Made Easy Test Series : Combinatory
Doubt: I eliminated half of the possibility from $\binom{24}{2}$ to remove t₁>t₂ and got the answer as 2070. Somebody, please explain why I am wrong and the solution is correct. [closed]

asked Dec 6, 2019 in Combinatory by Rudr Pawan (731 points) | 8 views

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Self doubt on counting
1.Number of Distributions of 5 books in 3 bookshelves such that each bookshelf get atleast 1 book 2.Number of Arrangement of 5 books in 3 bookshelves such that each bookshelf get atleast 1 book. I’m unable to understand the difference between Arrangements & Distributions. Can someone explain ?

asked Dec 5, 2019 in Combinatory by pranay562 (918 points) | 9 views

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self doubt-permutation and combination
Given 100 boys and 80 girls,how many possible arrangements are possible such that atmost 2 girls sit together?

asked Dec 3, 2019 in Combinatory by Doraemon (91 points) | 22 views

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ACE Material
Donuts come in 30 different varieties and Catherine wants to buy a dozen . How many choices does she have? Explain this please.

asked Dec 2, 2019 in Combinatory by teja1521 (8 points) | 6 views

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Applied course test series: Combinatorics
How to solve above type of questions? Is there any good tricks to solve above type questions.

asked Dec 1, 2019 in Combinatory by vishal burnwal (119 points) | 19 views

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1 answer

Mathematics Venn diagram
Of 30 Personal Computers owned by faculty members in a certain university department,20 run windows,eight have 21 inch monitors,25 have CD-ROM drives.20 have atleast two of these features and 6 have all the three features. How many PC’s have atleast one of these features? How many have none of these features? How many have exactly one feature? Anyone please clarify.

answered Nov 23, 2019 in Combinatory by Satbir (4.1k points) | 29 views

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No of binary trees with n labelled nodes
So I followed this link and have doubt regarding the no of ways of choosing edges with $n$ labelled nodes. Let's say I have 3 nodes - $A, B, C$ $l_X$ : left child of a node $X$ $r_X$ : right child of a node $X$ Now, any ... be considered that both $(l_A,r_A)$ and $(r_A,l_A)$ produces 1 unique binary trees each. Is this the correct way to think about this?

asked Nov 21, 2019 in Combinatory by avistein (355 points) | 16 views

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GENERATING FUNCTION: Kenneth Rosen
Find the generating function of the sequence 2, 4, 10, 28, 82, ……

answered Nov 18, 2019 in Combinatory by GAITONDE (1.7k points) | 15 views

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1 answer

MADE EASY TEST : DISCRETE MATHS
In how many ways 11 chocolates can be distributed to 7 children such that each one gets atleast one is ____

answered Oct 21, 2019 in Combinatory by GAITONDE (1.7k points) | 16 views

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Self Doubt : Integer Solution
Find the number of ways 5 dices can be rolled to get a sum of 25. While solving this question, the way we solve it is $x_1+x_2+x_3+x_4+x_5$ $=25$ where $1<=x_i<=6$ So we replace $x_i$ by $y_i =6-x_i$ , which is $x_i=6-y_i$ substituting ... first problem all the dices should have value $>0$ , so why in that case we haven't made $x_i=y_i+1$ for all the cases?

asked Oct 19, 2019 in Combinatory by Debapaul (620 points) | 43 views

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nptel assignment
I am getting answer 64 didn’t know how answer is 40

asked Oct 17, 2019 in Combinatory by Akanksha Agrawal (6 points) | 21 views

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Self Doubt: Number of integer solutions

asked Oct 5, 2019 in Combinatory by Debapaul (620 points) | 12 views

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madeeasy class notes(generating function)
get the generating function for x(1+x)(1-x)^3 .

asked Sep 20, 2019 in Combinatory by eyeamgj (27 points) | 10 views

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Problem on Probability
A set contain 5 distinct element .A one-one mapping is selected at random from A to A.Find the probability that number match to exactly itself.

answered Sep 15, 2019 in Combinatory by GAITONDE (1.7k points) | 20 views

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2 answers

Self doubt on permutations in.combinatorics
Let 7 digit no is to be made then find total no of ways If the no is divisible by 3 and repetition is allowed and zero is not used

answered Sep 1, 2019 in Combinatory by Bikram (1.2k points) | 27 views

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Binary String with 5 0's and 6 1's possible, where all 0's are together.

answered Aug 24, 2019 in Combinatory by Satbir (4.1k points) | 31 views

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jee practice ques permutation
There are 5 apples 10 mangoes and 15 oranges in a basket. Then find number of ways of distributing 15 fruits each to 2 persons. a)56 b)64 c)66 d)72

asked Aug 13, 2019 in Combinatory by Shubhm (23 points) | 11 views

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Self Doubt: Combinatorics
In how many ways a garland maker can stitch the flowers to make a garland with 4 red roses(distinct) and 10 white roses(distinct) so that no 2 red roses come together. My doubt is should we take (n-1)!/2 * 10P4 or (n-1)! * 10P4? As it is a case of non-living object y should we make distinction between clockwise and anticlockwise? (n-1)!/2 is more apt right?

answered Aug 10, 2019 in Combinatory by Satbir (4.1k points) | 61 views

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Combinatorics
What is the logic to solve this?

asked Aug 9, 2019 in Combinatory by Jean (8 points) | 17 views

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A person shops for 10 chocolates of 3 different types. How many selections of chocolates can he make?

answered Aug 8, 2019 in Combinatory by Satbir (4.1k points) | 70 views

+1 vote

1 answer

MadeEasy Workbook
in how many different ways can $8$ different shirts be distributed among $4$ different people so that each receives $2$ shirts.

answered Jul 17, 2019 in Combinatory by Debargha Bhattacharj (1.5k points) | 18 views

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# combinatorics
1) How many integers in the set {1,2,3,.....,1,00,000} contain exactly one 3, exactly one 4, exactly one 5 in their decimal representation?? 2) How many 4 digit integers are there with digit 6 exactly appearing once? 3) How many integers in the set {1,2,3,.....,1000} have distinct digits? Which type of approach is used to solve this type of questions??

asked Jul 12, 2019 in Combinatory by G Shaheena (8 points) | 23 views

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Allan Career Institute: Discrete Math
Let $f\left ( x\right )$ be continuous probability density function of a random variable $X.$ Then probability of $a\leq X< b$ is $A)f\left ( b \right )-f\left ( a \right )$ $B)f\left ( a-b \right )$ $C)\int_{b}^{a}xf\left ( x \right )dx$ $D)\int_{b}^{a}f\left ( x \right )dx$ Plz give some link for probability of pdf

asked Jul 7, 2019 in Combinatory by srestha (636 points) | 13 views

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Doubt on Stars and Bars Counting ROSEN Chapter 7 Advanced Counting

answered Jun 30, 2019 in Combinatory by Arkaprava (147 points) | 17 views

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Kenneth Rosen Edition-7 Chapter-6 Example-8
How many ways are there to distribute hands of 5 cards to each of four players from the standard deck of 52 cards? Why this question can not be solved using the category of COMBINATION WITH REPETITION? I was thinking four players as four boxes with each having 5 balls and 52 cards as 52 similar balls. Please someone clarify the mistake i am doing.

asked Jun 29, 2019 in Combinatory by Kushagra गुप्ता (175 points) | 14 views

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1 answer

combintorics--counting
How many bit strings contain exactly eight 0s and 10 1s if every 0 must be immediately followed by a 1?

answered Jun 17, 2019 in Combinatory by Arkaprava (147 points) | 11 views

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kenneth Rosen-chapter 5 -exercise from section 5.5

answered Jun 15, 2019 in Combinatory by Arkaprava (147 points) | 20 views

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Self Doubt (about combinatorics)
Question - In how many ways we can arange 8 boys & 5 girls such that no two girls sit together??? now in this type os qsn. why we're always taking this configuration - G B G B G B G B G B G B G B G B G (i.e here 1st 8 ... sit & then boys in middle) As the qsn. have not saying alternatively boys & girls, so what stops me to taking any of these approach??

answered Jun 15, 2019 in Combinatory by Arkaprava (147 points) | 11 views

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