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 :

Answer: Option A

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