Permutation and CombinationHard
Question
Let Tn be the number of all possible triangles formed by joining vertices of an n-sided regular polygon. If Tn+1 - Tn = 10, then the value of n is :
Options
A.7
B.5
C.10
D.8
Solution
Tn = nC3 ⇒ n+1C3 - nC3 = 10
(n + 1) n (n - 1) - n(n - 1) (n - 2) = 60
n(n - 1) = 20
n = 5
(n + 1) n (n - 1) - n(n - 1) (n - 2) = 60
n(n - 1) = 20
n = 5
Create a free account to view solution
View Solution FreeMore Permutation and Combination Questions
The number of numbers of 4 digits which are not divisible by 5 are (when repetition is allowed)-...Consider all the permutations of the word CORRUPTION. Number of words in which U appears prior to both R is equal to -...The number of signals that can be made with 3 flags each of different colour by hoisting 1 or 2 or 3 above the other, is...The number of ways in which 20 persons can sit on 8 chair round a circular table is-...In an examination, a candidate is required to pass in all the four subjects he is studying. The number of ways in which ...