Question

Find the number of triangles that can be formed using the vertices of an Octagon.

56

64

72

None of these


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Answer 1

answer : option (1) 56

explanation : we have to find number of triangles that can be formed using the vertices of an octagon.

This question is based on concept of permutation - combination.

use formula, ⁿCr [ choose r in a groups out of n. ]

here , choose 3 in a group (because triangle formed using three vertices ) out of 8. i.e., 8C3 = 8!/3!(8 - 3)! = 8!/(3! × 5!)

= 8 × 7 × 6 × 5!/(6 × 5!)

= 8 × 7

= 56

hence, number of triangles should be 56.

[note : you can also use the formula, n(n -1)(n - 2)/6 ]

Answer 2

Answer:

56 ideas the answer hope it helps