Question:
The measure of angles of a hexagon are x°, (x − 5)°, (x − 5)°, (2x − 5)°, (2x − 5)°, (2x + 20)°. Find the value of x.
Solution:
Since the sum of all the angles of a hexagon is $720^{\circ}$, we get:
$x^{\circ}+(x-5)^{\circ}+(x-5)^{\circ}+(2 x-5)^{\circ}+(2 x-5)^{\circ}+(2 x+20)^{\circ}=720^{\circ}$
$\Rightarrow x^{\circ}+x^{\circ}-5^{\circ}+x^{\circ}-5^{\circ}+2 x-5^{\circ}+2 x-5^{\circ}+2 x+20^{\circ}=720^{\circ}$
$\Rightarrow 9 x-20^{\circ}+20^{\circ}=720^{\circ}$
$\Rightarrow 9 x=720^{\circ}$
$\therefore x=80$