## Calculus (3rd Edition)

$\frac{1}{\pi}.$
The average is given by $$\frac{1}{2-1} \int_{1}^{2} \frac{\sin (\pi / x)}{x^{2}} d x=\frac{1}{\pi} \int_{\pi / 2}^{\pi} \sin u d u=-\left.\frac{1}{\pi} \cos u\right|_{\pi / 2} ^{\pi}=\frac{1}{\pi}.$$