1. **Problem statement:** We have a fan with radius $30$ cm and $4$ blades, each blade subtending a central angle of $30^\circ$. We need to find the total area covered by the $4$ blades in terms of $\pi$. 2. **Formula used:** The area of a sector of a circle is given by $$\text{Area of sector} = \frac{\theta}{360^\circ} \times \pi r^2$$ where $\theta$ is the central angle in degrees and $r$ is the radius. 3. **Calculate the area of one blade:** $$\text{Area of one blade} = \frac{30}{360} \times \pi \times 30^2 = \frac{1}{12} \times \pi \times 900 = 75\pi$$ 4. **Calculate the total area of 4 blades:** $$\text{Total area} = 4 \times 75\pi = 300\pi$$ 5. **Final answer:** The area covered by the 4 blades is $$300\pi \text{ cm}^2$$