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प्रश्न
A cylindrical vessel open at the top has diameter 20 cm and height 14 cm. Find the cost of tin-plating it on the inside at the rate of 50 paise per hundred square centimetre.
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उत्तर
\[\text{ Given } : \]
\[\text{Diameter, d = 20 cm} \]
\[\text{ Radius, r = 10 cm } \]
\[\text{ Height, h = 14 cm} \]
\[\text{ Area inside the cylindrical vessel that is to be tin - plated } = S\]
\[S = 2\pi rh + \pi r^2 \]
\[ = 2\pi \times 10 \times 14 + \pi \times {10}^2 \]
\[ = 280\pi + 100\pi\]
\[ = 380 \times \frac{22}{7} {cm}^2 \]
\[ = \frac{8360}{7} {cm}^2 \]
\[\text{ According to question: } \]
\[\text{ Cost per 100 {cm } }^2 = 50 \text{ paise } \]
\[\text{ Cost per {cm} } ^2 = Rs 0 . 005\]
\[\text{ Cost of tin - plating the area inside the cylindrical vessel } = Rs 0 . 005 \times \frac{8360}{7}\]
\[ = Rs \frac{41 . 8}{7} = Rs 5 . 97\]
\[\]
