A toy is made in the shape of a hemisphere of diameter 7 cm surmounted by a cone. If this 15.5 cm high toy is polished at 20 paise per cm2, then find the cost of polishing. (Take $π=\frac{22}{7}$)
Answer & explanation
Correct answer: option 3
Radius of hemisphere = \(\frac{7}{2}\) = 3.5 cm
Height of cone = 15.5 - 3.5 = 12 cm
l² = r² + h² ( l = slant height )
= 3.5² + 12 ²
= 12.25 + 144
l = 12.5 cm
Surface area of toy = surface area of hemisphere + surface area of cone
= 2× π× r² + π× r × l
= π× r ( 2r + l )
= \(\frac{22}{7}\) × 3.5 (7 + 12.5)
= 22 × 0.5 × 19.5
= 214.5cm2
toy is polished at 20 paise per cm2
Total cost of polishing = 214.5 × \(\frac{20}{100}\)
= Rs. 42.90