Question

Find the number of coins , 1.5cm in diameter and 2mm thick, to be melted to form a right circular cylinder of radius 2.25cm and height 10cm.

Answer 1

Each one of those coins is also a cylinder (just a very very short one), and its volume is
V = π r² h = π(.75)²(.2) = 9(π/80) cm³
The right circular cylinder has volume V = π(2.25)²(10) = 405π/8 cm³.

Divide the larger cylinder's volume by the volume of each coin = (405π/8) / (9π/80) = 450 coins