The water pipe is a cylinder. The question asks for the circular cross section of the pipe. We know the diameter is 20 cm. The radius is half of the diameter, so it is 10 cm. The area of the circular cross section is [tex]A= \pi r^2[/tex] We plug in r in our equation to get
[tex]A=\pi (10)^2=100 \pi[/tex]
100 [tex] \pi [/tex] cm^2 is our answer.
