Question

If the side of a cube is increased by 5%, then the surface area of a cube is increased by

• A. 0.1
• B. 0.6
• C. 0.06
• D. 0.2

Answer 1

Answer: (A)

0.1

Answer 2

Let one side of the cube be $x$ and surface area be $A$ So, $dx =5 \%=5 x / 100$ Then, $A=(6 x)^{2}$ $\Rightarrow dA / dx =12 x$ $\Rightarrow d A =(12 x ) d x$ $\Rightarrow dA =(12 x )(5 x / 100)$ $\Rightarrow d A =10 A / 100$ $\Rightarrow dA =10 \%$