Question

How many silver coins, 1.75 cm in diameter and of thickness 2 mm, must be melted to form a cuboid of dimensions $5.5cm\times 10cm\times 3.5cm?$

Answer 1

Radius of coin = 0.875 cm, height = 0.2 cm (10mm = 1cm)
Dimensions of cuboid $=5.5cm\times 10cm\times 3.5cm$
Volume of coin
$=\pi r^{2}h$
$=\pi \times {0.875}^2\times 0.2$
$=0.48125c{m}^2$
Volume of cuboid$=5.5\times 10\times 3.5=192.5c{m}^3$
(Volume of cuboid$=l\times b\times h$)
Number of coins
$=\frac{192.5}{0.48125}=400$