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
39