Answer
$10^{5}~seats$
Work Step by Step
Imagine two concentric circles of radius $r_{1}=60~m$ and $r_{2}=80~m$. The seats are in the region between the circumferences of the circles. We estimate that there are five seats per $m^{2}$.
Let $A_{1}$ be the area of the circle 1, $A_{2}$ be the area of the circle 2 and $A$ the area between the circumferences of the circles:
$A=A_{2}-A_{1}=π(r_{2})^{2}-π(r_{1})^{2}=π[(80~m)^{2}-(60~m)^{2}]\approx8800~m^{2}$
$8800~m^{2}=(8800~m^{2})(\frac{5~seats}{1~m^{2}})=44,000~seats=4.4\times10^{4}\approx10^{5}~seats$.
Notice that $4.4\gt\sqrt 10$.
