Q39 of 107 Page 16

How many coins 1.75 cm in diameter and 2 mm thick must be melted to form a cuboid 11 cm × 10 cm × 7 cm?

Volume of cuboid = l × b × h = 11 × 10 × 7


Diameter of coin = 1.75 cm


Radius cm = 0.875 cm


Thickness of coin =2 mm = 0.2 cm


Volume of coin (cylinder)


= (22/7) × 0.875 × 0.875 × 0.2 cm3


Let number of coins be n


⇒ n × volume of coins = volume of cuboid


⇒ n × (22/7) × 0.875 × 0.875 × 0.2 = 11 × 10 × 7



⇒ n = 1600


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