Question

How many quadrilaterals can be formed by joining the vertices of an octagon?

• A. $65$
• B. $60$
• C. $70$
• D. $64$

Answer 1

Answer: (C)

$70$

Octagon Number of sides $=n=8$

For quadrilatral there are only four sides

There should be a selection of four ponts and arranging of quadrilatral

${\Rightarrow }^8{C}_4=\frac{8!}{4!\times 4!}\Rightarrow \frac{8\times 7\times 6\times 5}{4\times 3\times 2}\Rightarrow 70quadrilatrals$

Option $:C$