Given that diameter of solid cylinder =2cm

Given that solid cylinder is recast to hollow cylinder

Length of hollow cylinder =16cm

External diameter = 20cm

Thickness = 2.5mm= 0.25cm

Radius of cylinder =1cm

So volume of solid cylinder=π(1)^{2} h ........(1)

Let length of solid cylinder be h

Thickness = R - r

0.25 = 10 - r

Internal radius = 9.75cm

So volume of hollow cylinder =π16(100 -95.0625) ......(2)

Volume of solid cylinder is equal to volume of hollow cylinder.

(1) = (2)

Equating equations (1) and (2)