We know that $360^{\circ} = 2\pi \text{ rad}$, so $1^{\circ} = \frac{\pi}{180} \text{ rad} \approx 1.745 \times 10^{-2} \text{ rad}$. Since $1$ minute of an arc ($1'$) is $\frac{1}{60}$ of a degree: $1' = \frac{1^{\circ}}{60} = \frac{1.745 \times 10^{-2}}{60} \text{ rad} \approx 2.908 \times 10^{-4} \text{ rad}$. Rounding off to three significant figures, we get $1' \approx 2.91 \times 10^{-4} \text{ rad}$.