Question

A decagon has angles that measure 156°, 135°, 147°, 160°, 116°, 150°, 150.2°, 119.2°, 146.6°, and z. What is z?

Answer 1

bearing in mind that the sum of all interior angles in a polygon is

180(n - 2)    n = number of sides in the polygon

a DECAgon, DECA=10, has 10 sides, and thus the sum of all its interior angles is 180(10 - 8) = 1440.

$\bf 156+135+147+160+116+150+150.2+119.2+146.6+z=1440 \\\\\\ 1280+z=1440\implies z=1440-1280\implies z=160$