# Q : 5    A hemispherical bowl made of brass has inner diameter $\small 10.5\hspace{1mm}cm$. Find the cost of tin-plating it on the inside at the rate of  Rs 16 per $\small 100\hspace{1mm}cm^2$.

H Harsh Kankaria

Given,

The inner radius of the hemispherical bowl = $r = \frac{10.5}{2}\ cm$

We know,

The curved surface area of a hemisphere = $2\pi r^2$

$\therefore$ The surface area of the hemispherical bowl = $2\times\frac{22}{7}\times\left (\frac{10.5}{2} \right )^2$

$=11\times1.5\times10.5$

$= 173.25 \ cm^2$

Now,

Cost of tin-plating $\small 100\hspace{1mm}cm^2$ =  Rs 16

$\therefore$ Cost of tin-plating $\small 33\hspace{1mm}cm^2$ =  $\small \\ Rs. \left (\frac{16}{100}\times173.25 \right )$

$\small = Rs. 27.72$

Therefore, the cost of tin-plating it on the inside is $\small Rs. 27.72$

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