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
150 students take admission. They are to be put in three sections A, B,C of equal size. The number of ways in which this...For what value of r, nPr = 720 and nCr = 120 ?...A coin is tossed 10 times. In how many different ways can we obtain 5 head and 5 tail-...nPn is equal to-...The number of words which can be formed using 4 letters of the word ′EXAMINATION′ is-...