logo

Ask Questions, Get Answers

 
X
 Search
Want to ask us a question? Click here
Browse Questions
Ad
Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
0 votes

The number of diagonals in a octagon will be

$\begin{array}{1 1}(A)\;28\\(B)\;20\\(C)\;10\\(D)\;16\end{array} $

Can you answer this question?
 
 

1 Answer

0 votes
Toolbox:
  • $C(n,r)=\large\frac{n!}{r!(n-r)!}$
In a octagon there are eight sides and eight points.The diagonal will be formed by joining any two points except the sides.
$\therefore$ Required number of ways =$8C_2-8$
$8C_2=\large\frac{8!}{2!6!}$
$\Rightarrow \large\frac{8\times 7\times 6!}{2\times 6!}$
$\Rightarrow 28$
$8C_2-8=28-8$
$\Rightarrow 20$
Hence (B) is the correct answer.
answered Jun 20, 2014 by sreemathi.v
 

Related questions

Ask Question
student study plans
x
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App
...