Question

A hollow sphere of outer radius of 4 cm and thickness of 3 cm is to be made from metal. What is the total amount of metal required (in cm^3) to make the sphere? (Take π = \(\frac{22}{7}\))

(a) 281

(b) 264

(c) 225

(d) 227

The question was posed to me during an online interview.

I want to ask this question from Volume of a Sphere topic in portion Surface Areas and Volumes of Mathematics – Class 9

Answer 1

The correct answer is (b) 264

The best I can explain: Outer radius ro = 4cm

Inner radius ri = outer radius – thickness

= 4 – 3

ri = 1cm

This means that the sphere is hollow and volume of metal required = \(\frac{4}{3} πr_o^3 – \frac{4}{3} πr_i^3\)

= \(\frac{4}{3} π (4^3 – 1^3)\)

= \(\frac{4*22*63}{3*7}\)

= 264 cm^3.