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 $π=\frac{22}{7}$)

₹42.90

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