# PERMUTATION & COMBINATION | IIT JEE CONCEPTS | Part 10 | JEE Main 2013 | Count Number of Triangles - Videos

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In this video, we will learn an important concept of counting the number of triangles in two cases:
(i) When all the points given are non-collinear
(ii) When some of the points or a set of points are collinear

Questions Discussed
JEE Main 2013
Let Tn be the possible number of triangles formed by joining the vertices of a n-sided regular polygon. If Tn+1 – Tn = 10, then the value of n is
(A) 7 (B) 5 (C) 10 (D) 8

JEE Main 2013 Online
On sides AB, BC and AC of a triangle ABC, 3, 4, 5 distinct points (excluding vertices) are chosen. The number of triangles that can be constructed using these points as vertices are
(A) 210 (B) 205 (C) 215 (D) 220

TRY YOURSELF Questions
Question 1
Let Tn be the possible number of triangles formed by joining the vertices of a n-sided regular polygon. If Tn+1 – Tn = 21, then the value of n is
(A) 5 (B) 4 (C) 6 (D) 7

Question 2
If 7 points out of 12 lie on a single straight line, then the number of triangles formed is
(A) 19 (B) 185 (C) 201 (D) 205

Question 3
4 points out of 8 points in a plane are collinear, then the number of different quadrilateral that can be formed by joining them is
(A) 53 (B) 56 (C) 76 (D) 60

Permutation and Combination IIT JEE Concepts Playlist Link