Question

The number of coins, of radius 0.75 and thickness 0.2 cm to be melted to make a right circular cylinder of height 8 cm and radius 3 cm is

• A. 640
• B. 650
• C. 675
• D. 700

Answer 1

The correct option is A 640

Given radius of coin is 0.75 cm and thickness is 0.2 cm and radius of right circular cylinder is 3 cm and 8 cm

Then volume of coin =$\pi r^{2}t=\pi (0.75{)}^2\times 0.2=0.1125\pi c{m}^3$

And volume of right circular cylinder =$\pi r^{2}h=\pi (3{)}^2\times 8=72\pi c{m}^3$

Then no of coin made by melted cylinder=$\frac{72\pi }{0.1125\pi }=640$