Question

Find the number of coiins of radius 0.75cm and thickness 0.2cm.That should be melted to make a right cylinder of height 8cmand of radius3cm

Answer 1

Clearly, 'n' number of coins should be melted to make a cylinder.

∴ By formula,

n × Volume of coin = Volume of cylinder.  → 1

COIN:-

radius = r = 0.75cm

thickness = height = h = 0.2cm

CYLINDER:-

radius = R = 3cm

height = H = 8cm

[In both the cases, they are cylindercal in shape]

n = ?

Sub. in 1,

n × πr²h = πR²H

n × r²h = R²H                   [Striking π as it is common]

n × 0.75 × 0.75 × 0.2 = 3 × 3 × 8

      n × 0.5625 × 0.2 = 9 × 8

                  n × 0.1125 = 72

                                 n = 72 ÷ 0.1125

                               ∴n = 640

∴640 coins should be metled to form a cylinder.