How many silver coins 1.75cm in …

For a silver coin Diameter = 1.75 cm
{tex}\therefore {/tex} Radius (r)={tex}\frac{{1.75}}{2}cm = \frac{7}{8}cm{/tex}
Thickness (h) = 2 mm ={tex}\frac{1}{5}cm{/tex}

{tex}\therefore {/tex} The volume of a silver coin
={tex}\pi {r^2}h = \pi {\left( {\frac{7}{8}} \right)^2}\left( {\frac{1}{5}} \right){/tex}
={tex}\frac{{49}}{{320}}\pi c{m^3}{/tex}
Let n coins be melted.
Then, volume of n coin={tex}n\frac{{49}}{{320}}\pi c{m^3}{/tex}
For cuboid
length(L) = 5.5 cm
breath(B) = 10 cm
height(H) = 3.5 cm
{tex}\therefore {/tex} The volume of the cuboid = lbh
=5.5 × 10 × 3.5=192.5
={tex}\frac{{1925}}{{10}} = \frac{{385}}{2}{/tex}cm²
According to the question,
{tex}n\frac{{49\pi }}{{320}} = \frac{{385}}{2} \Rightarrow n = \frac{{385}}{2}.\frac{{320}}{{49\pi }}{/tex}
{tex}\Rightarrow {/tex} {tex}n = \frac{{385}}{2}.\frac{{320}}{{49}}.\frac{7}{{22}} \Rightarrow n = 400{/tex}
Hence, 400 coins must be melted