The interior angles of a convex polygon are in arithmetic progression. The smallest angle is 120 degrees and the common difference is 5 degrees. Find the number of sides of the polygon.
+2668 ***EDIT***
I forgot to write the arithmetic series part correctly. The equation should be:
180(s−2)=s(120+(120+5(s−1))2
Solving, we find it can be 9, or 16. It can't be 16, because the largest angle is greater than 180, and then it would not be a convex polygon.
Thus, the CORRECT answer is 9
Thank You Geno for telling me!!!
