Question

A steel pipe has an outside diameter (OD) of $100mm$ and an inside diameter (ID) of $80mm$, what is the area of the cross section (to nearest mm${}^2$)?

Answer 1

The area of circle with diameter $100mm$ is $\pi \times {50}^2=2500\pi$

The area of circle with diameter $80mm$ is $\pi \times {40}^2=1600\pi$

The required area is $2500\pi -1600\pi =900\pi =2827$