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on increasing each of the radius of the base and the height of a cone by 20%.its volume will be increased by : a)50% b)25% c)72.8% d)40%

initial radius of cone = r
final radius = 6/5r
initial height = h 
final height = 6/5h
initial volume = 1/3?r2h
final volume = 1/3. ? . 6/5r . 6/5r . 6/5 h = 216/125 . 1/3?r2h = 1.728 . ?r2h
Hence Change in volume = [1.728 - 1] X 100 = 72.8 %