Advertisements
Advertisements
प्रश्न
If nC4 , nC5 and nC6 are in A.P., then find n.
उत्तर
Since nC4 , nC5 and nC6 are in AP.
∴ 2. nC5 = nC4 + nC6
\[ \Rightarrow \frac{2}{5 \times 4!\left( n - 5 \right)\left( n - 6 \right)!} = \frac{1}{4!\left( n - 5 \right)\left( n - 4 \right)\left( n - 6 \right)!} + \frac{1}{6 \times 5 \times 4!\left( n - 6 \right)!}\]
\[ \Rightarrow \frac{2}{5\left( n - 5 \right)} = \frac{1}{\left( n - 5 \right)\left( n - 4 \right)} + \frac{1}{30}\]
\[ \Rightarrow \frac{2}{5\left( n - 5 \right)} - \frac{1}{\left( n - 5 \right)\left( n - 4 \right)} = \frac{1}{30}\]
\[ \Rightarrow \frac{2n - 8 - 5}{5\left( n - 5 \right)\left( n - 4 \right)} = \frac{1}{30}\]
\[ \Rightarrow \frac{2n - 13}{\left( n - 5 \right)\left( n - 4 \right)} = \frac{1}{6}\]
\[ \Rightarrow 12n - 78 = n^2 - 9n + 20\]
\[ \Rightarrow n^2 - 21n + 98 = 0\]
\[ \Rightarrow \left( n - 7 \right)\left( n - 14 \right) = 0\]
\[ \therefore n = 7 \text{and} 14\]
APPEARS IN
संबंधित प्रश्न
Determine n if `""^(2n)C_3 : ""^nC_3 = 11: 1`
Determine the number of 5-card combinations out of a deck of 52 cards if each selection of 5 cards has exactly one king.
Compute:
(i)\[\frac{30!}{28!}\]
How many three-digit numbers are there with no digit repeated?
Evaluate the following:
n + 1Cn
If 28C2r : 24C2r − 4 = 225 : 11, find r.
In how many ways can a football team of 11 players be selected from 16 players? How many of these will
include 2 particular players?
From a class of 12 boys and 10 girls, 10 students are to be chosen for a competition; at least including 4 boys and 4 girls. The 2 girls who won the prizes last year should be included. In how many ways can the selection be made?
A sports team of 11 students is to be constituted, choosing at least 5 from class XI and at least 5 from class XII. If there are 20 students in each of these classes, in how many ways can the teams be constituted?
A candidate is required to answer 7 questions out of 12 questions which are divided into two groups, each containing 6 questions. He is not permitted to attempt more than 5 questions from either group. In how many ways can he choose the 7 questions?
A committee of 3 persons is to be constituted from a group of 2 men and 3 women. In how many ways can this be done? How many of these committees would consist of 1 man and 2 women?
A committee of 7 has to be formed from 9 boys and 4 girls. In how many ways can this be done when the committee consists of: at least 3 girls?
Out of 18 points in a plane, no three are in the same straight line except five points which are collinear. How many (i) straight lines
Find the number of combinations and permutations of 4 letters taken from the word 'EXAMINATION'.
A tea party is arranged for 16 persons along two sides of a long table with 8 chairs on each side. Four persons wish to sit on one particular side and two on the other side. In how many ways can they be seated?
If 20Cr + 1 = 20Cr − 1 , then r is equal to
The number of parallelograms that can be formed from a set of four parallel lines intersecting another set of three parallel lines is
Find n and r if `""^"n""P"_"r"` = 720 and `""^"n""C"_("n" - "r")` = 120
There are 3 wicketkeepers and 5 bowlers among 22 cricket players. A team of 11 players is to be selected so that there is exactly one wicketkeeper and at least 4 bowlers in the team. How many different teams can be formed?
Five students are selected from 11. How many ways can these students be selected if two specified students are not selected?
Four parallel lines intersect another set of five parallel lines. Find the number of distinct parallelograms that can be formed.
In a small village, there are 87 families, of which 52 families have atmost 2 children. In a rural development programme 20 families are to be chosen for assistance, of which atleast 18 families must have at most 2 children. In how many ways can the choice be made?
A boy has 3 library tickets and 8 books of his interest in the library. Of these 8, he does not want to borrow Mathematics Part II, unless Mathematics Part I is also borrowed. In how many ways can he choose the three books to be borrowed?
All the letters of the word ‘EAMCOT’ are arranged in different possible ways. The number of such arrangements in which no two vowels are adjacent to each other is ______.
A box contains two white, three black and four red balls. In how many ways can three balls be drawn from the box, if atleast one black ball is to be included in the draw
A convex polygon has 44 diagonals. Find the number of its sides.
A bag contains six white marbles and five red marbles. Find the number of ways in which four marbles can be drawn from the bag if they can be of any colour
In how many ways can a football team of 11 players be selected from 16 players? How many of them will include 2 particular players?
A group consists of 4 girls and 7 boys. In how many ways can a team of 5 members be selected if the team has at least three girls.
The number of triangles that are formed by choosing the vertices from a set of 12 points, seven of which lie on the same line is ______.
The number of ways in which a team of eleven players can be selected from 22 players always including 2 of them and excluding 4 of them is ______.
Three balls are drawn from a bag containing 5 red, 4 white and 3 black balls. The number of ways in which this can be done if at least 2 are red is ______.
To fill 12 vacancies there are 25 candidates of which 5 are from scheduled castes. If 3 of the vacancies are reserved for scheduled caste candidates while the rest are open to all, the number of ways in which the selection can be made is 5C3 × 20C9.
There are 15 players in a cricket team, out of which 6 are bowlers, 7 are batsmen and 2 are wicketkeepers. The number of ways, a team of 11 players be selected from them so as to include at least 4 bowlers, 5 batsmen and 1 wicketkeeper, is ______.
Total number of 6-digit numbers in which only and all the five digits 1, 3, 5, 7 and 9 appear is ______.
The number of numbers between 2,000 and 5,000 that can be formed with the digits 0, 1, 2, 3, 4, (repetition of digits is not allowed) and are multiple of 3 is?
There are ten boys B1, B2, ...., B10 and five girls G1, G2, ...., G5 in a class. Then the number of ways of forming a group consisting of three boys and three girls, if both B1 and B2 together should not be the members of a group is ______.
The number of words, with or without meaning, that can be formed by taking 4 letters at a time from the letters of the word 'SYLLABUS' such that two letters are distinct and two letters are alike is ______.
