A cylindrical pipe has internal radius $4$ cm, external radius $5$ cm and length $20$ cm. The volume of…

A cylindrical pipe has internal radius $4$ cm, external radius $5$ cm and length $20$ cm. The volume of metal used is (use $\pi=\dfrac{22}{7}$):
  1. $\dfrac{3960}{7} \text{ cm}^{3}$
  2. $\dfrac{1980}{7} \text{ cm}^{3}$
  3. $\dfrac{2200}{7} \text{ cm}^{3}$
  4. $1100 \text{ cm}^{3}$

Solution

Volume of metal $= \pi (R^{2} - r^{2}) h = \dfrac{22}{7}(25-16)(20) = \dfrac{22}{7} \times 9 \times 20 = \dfrac{3960}{7} \text{ cm}^{3} \approx 565.71 \text{ cm}^{3}$.

Asked in: IMO

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