Four angles of a polygon are 100� each. The remaining angles are 160� each. Find the number of sides of the polygon.

Let n be the number of sides:

Sum of all interior angles of a polygon = (n – 2) 180o

Four angles measure 100o each and remaining angles (i.e n – 4) measure 160o each

100(4+(n-4) *160 = (n-2)180

400+160n-640 = 180n – 360

760-640 = 20n

n = 6

Hence the number of sides of the polygon = 5=6