JAMB Mathematics 2021 Paper

Concept:The volume of metal used is the difference between the external and internal volumes of the cylindrical pipe.Explanation:First, convert the pipe length to centimetres: $3\text{m} = 300\text{cm}$.Internal radius $r = 10\text{cm}$.The metal is $3\text{cm}$ thick, so external radius $R = 10 + 3 = 13\text{cm}$.Volume of a cylinder is given by $\pi r^2 h$.External volume $= \pi \times 13^2 \times 300$.Internal volume $= \pi \times 10^2 \times 300$.Volume of metal $=$ External volume $-$ Internal volume.So, volume of metal $= \pi(13^2 - 10^2) \times 300$.$= \pi(169 - 100) \times 300$.$= \pi \times 69 \times 300$.$= 20700\pi\text{cm}^3$.Answer:D. $20700\pi\text{cm}^3$.