The external and the internal radii of a hollow cylinder of height 15 cm are 6.75 cm and 5.25 cm respectively. If it is melted to form a solid cylinder of height half of the orignal cylinder, then the radius of the solid cylinder is?
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Correct answer: A
Explanation
The correct answer is option 1 i.e. 6 cm
Volume of hollow cylinder = Volume of solid cylinder
π[(6.75)2 - (5.25)2] × 15 = πr2 × 15/2
⇒ [(27/4)2 - (21/4)2] × 15 = r2 × 15/2
⇒ [729/16 - 441/16] × 2 = r2
⇒ [288/16] × 2 = r2
⇒ r2 = 36
⇒ r = 6 cm