Q13 of 44 Page 14

A decorative block as shown in the given figure is made of a cube and a hemisphere. The edge of the cube is 10cm, and the radius of the hemisphere attached on the top is 3.5. Find the cost of painting the block at the rate of 50 paise per sq.cm.


Given that side of a cube = 10cm


Total Surface Area of cube = 6(side)2


= 6 × 10 × 10


= 600cm2


Now, Radius of hemisphere = 3.5cm


Curved Surface Area of hemisphere = 2πr2


= 77cm2


Base area of hemisphere = Area of circle = πr2



= 38.5cm2


Therefore,


Total Surface Area of block = Total Surface area of a cube + CSA of the hemisphere - Base area of a hemisphere


= 600 + 77 – 38.5


= 638.5cm2


Cost of painting the block of 1cm2 = Rs 0.50


Cost of painting the block of 638.5cm2 = Rs 0.50 × 638.5


= Rs 319.25


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