Q22 of 68 Page 341

How many triangles can be formed in a decagon?

Total number of sides in a decagon = 10


We know that number of vertices in triangle = 3


So, out of 10 vertices we have to choose 3 vertices.


Therefore,


Total number of triangles in a decagon = 10C3


Total number of triangles = 120


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20

Find the number of diagonals of

(i) a hexagon,


(ii) a decagon,


(iii) a polygon of 18 sides


 21

How many triangles can be obtained by joining 12 points, four of which are collinear?

 23

How many different selections of 4 books can be made from 10 different books, if

(i) there is no restriction?


(ii) two particular books are always selected?


(iii) two particular books are never selected?


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How many different products can be obtained by multiplying two or more of the numbers 3, 5, 7, 11 without repetition?