Question

how many coins 1.75cm in diameter and of thickness 2mm must be melted to form a cuboid of dimensions 11cmx10cmx7cm

Answer 1

let no.of coins be n
given:
dimensions of coin( cylinder),
d= 1.75cm
h= 2mm
dimensions of cuboid,
11cm×10cm×7cm
To find :
n
solution:
h is 2mm or h= 0.2cm or 2/ 10 cm
n = vol of cuboid / vol of coin
vol of coin:

$\pi r {}^{2} h$
vol of cuboid:
$l \times b \times h$
therefore,
n= (l×b×h)/pi× r^2×h
n=(11×10×7)/[( 22/7)×(1.75/2)×(1.75/2)×(2/10)]
n=[770]/(0.48125)
n= 1600 coins
therefor the no.of coins = 1600