## Elementary Technical Mathematics

$A=1.32~in^{2}$
The area of the cross-section of the pipe can be calculated with the formula $A=\frac{\pi}{4}d^{2}$. We apply the formula with the outside and inside diameters, and subtract: $A=\frac{\pi}{4}d_{out}^{2}-\frac{\pi}{4}d_{in}^{2}$ Where $d_{out}=3.50in$ $d_{in}=3.25in$ So, $A=\frac{\pi}{4}d_{out}^{2}-\frac{\pi}{4}d_{in}^{2}=\frac{\pi}{4}(3.50in)^{2}-\frac{\pi}{4}(3.25in)^{2}=1.32~in^{2}$