The metal to be used for covering a cylinder having external radius 5 cm, height 21 cm and thickness I cm is to be cast from a cylinder. What should be the height of the cylinder of radius 3 cm from which this casting can be done?

Options

A. 12 cm
B. 39 cm
C. 21 cm
D. 20 cm

Answer

C

Explanation

Volume of metal to be casted `=(22//7)xx[(5)^2-(4)^2]xx21`
So, `(22//7)xx3^2xxh=(22//7)xx[(5)^2-(4)^2]xx21`
Solve, h = 21