6. How many silver coins, 1.75 cm in diameter and of thickness 2 mm, must be melted to form a cuboid of dimensions 5.5 cm × 10 cm × 3.5 cm?
Let us assume the number of coins that need to be melted be n.
Then we can write :
The volume of n coins = Volume of cuboid formed.
Thus the required number of coins is 400.