A hemispherical bowl has 3.5 cm radius. It is to be painted inside as well as outside. The cost of painting it at the rate of Rs. 5 per 10 sq. cm will be :

A. Rs. 77

B. Rs. 100

C. Rs. 175

D. Rs. 50

Answer: Option A

Solution(By Examveda Team)

Radius of a hemispherical bowl = 3.5 cm
Inner and outer surface area of the bowl :
$$\eqalign{ & = 4\pi {r^2} \cr & = 4 \times \frac{{22}}{7} \times 3.5 \times 3.5 \cr & = 154{\text{ sq}}{\text{.cm}} \cr} $$
Total cost of painting at the rate of Rs. 5 per 10 sq.cm :
$$\eqalign{ & = 154 \times \frac{5}{{10}} \cr & = {\text{Rs}}{\text{. 77}} \cr} $$