The value of 400 + 0.0400 + 0.000004 = ?

Answer: Option C

$$\begin{array}{rl}& \text{According to question,}\\ & \sqrt{400}+\sqrt{0.0400}+\sqrt{0.000004}\\ & \Rightarrow 20+0.2+0.002\\ & \Rightarrow 20.202\end{array}$$