Answer
$\frac{5\pi}{9}$ rad.
Work Step by Step
Use the conversion $360^\circ=2\pi \, \textrm{rad.}$ to simplify the expression to $$100^\circ \cdot \frac{2\pi \, \textrm{rad.}}{360^\circ}=\frac{100\pi}{180} \, \textrm{rad.}=\frac{5\pi}{9} \, \textrm{rad.}$$