The rain water from a roof 22 m × 20 m drains into a cylindrical vessel having a diameter of 2 m and height 3.5 m. If the vessel is just full, then the rainfall (in cm) is:

Answer: Option B

Volume of vessel = Volume of roof
π × r² × h = 22 × 20 × x   (where x is rainfall in cm)
$$\begin{array}{rl}& \Rightarrow \frac{22}{7}\times \frac{100\times 100\times 350}{22\times 20\times 100\times 100}=\text{x}\\ & \Rightarrow \text{x}=2.5\text{ cm}\end{array}$$