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 :
Options:
A . Rs. 77
B . Rs. 100
C . Rs. 175
D . Rs. 50
Answer: Option A 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 : $$\eqalign{ & = 154 \times \frac{5}{{10}} \cr & = {\text{Rs}}{\text{. 77}} \cr} $$
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