The diameter of the silver coin is 2r = 1.75 cm.
Therefore, the radius of the silver coin is r = \(\frac{1.75}{2}\) = 0.875 cm.
The area of the silver coin is \(\pi r^2\) = 0.875 × 0.875\(\pi\) = 0.765625 \(\pi\) cm2 = 2.40625 cm2 .
Since, given that the thickness of the coin is d = 2 mm = 0.2 cm.
Therefore, the volume of silver coin = Area of the coin × thickness of the coin
= 2.40625 × 0.2 = 0.48125 cm3.
Since we are forming a cuboid of dimensions 5.5 cm × 10 cm × 3.5 cm from n number of silver coins.
Therefore, the volume of the cuboid = n × the volume of a silver coin.
⇒ 5.5 × 10 × 3.5 = 0.48125 n (∵ volume of the cuboid = lbh)
⇒ n = \(\frac{ 5.5 × 10 × 3.5}{0.48125}\) =\(\frac{192.5}{0.48125}\) = 400
Hence, total 400 silver coin must be melted to form a cuboid of dimension 5.5 cm × 10 cm × 3.5 cm.
