Question

Find the number of coins, 2cm in diameter and 0.2cm thick to be melted to form a right circular cylinder of height 5cm and radius 4cm.

Answer 1

Radius of the coin =1cm || N be the no. of
Thickness or height =2/10cm coins
N*Vol. of cylinder = Vol. Of of big cylinder
N*22/7*1*1*2/10=22/7*4*4*5
N*1/10=40
N =400
400 coins are needed

Answer 2

For the bigger cylinder,
Height , H = 5 cm
Radius , R = 4cm
It's volume = πR²H
= 22/7 * 4* 4* 5
= 1760/7 cm³
Diameter of 1 coin = 2 cm
Its radius, r = 1 cm
It's height , h = 0.2 cm
Volume of 1 coin = πR²H
= 22/7 * 1 * 1 * 0.2
= 44/70 cm³
Let the number of coins required be n
Therefore, volume of bigger cylinder = volume of 1 coin x n
= 1760/7 = n * 44/70
= 44 n = 1760 * 10
= 44 n = 17600
n = 17600/44
n = 400
Hence, 400 coins are required.