The area of two similar triangles are 12 cm2 and 48 cm2. If the height of the smaller one is 2.1 cm, then the corresponding height of the bigger one is :

Answer: Option B

Note : The areas of two similar triangles are in the ratio of the squares of the corresponding altitudes. Let the length of the required altitude be x cm
Then,
$$\begin{array}{rl}& \frac{12}{48}=\frac{{\left(2.1\right)}^2}{x^2}\\ & \Rightarrow x^2=\left(4.41\times 4\right)\\ & \Rightarrow x=2.1\times 2\\ & \Rightarrow x=4.2cm\end{array}$$