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A hollow cylindrical tube 20 cm long is made of iron and its external and internal diameters are 8 cm and 6 cm respectively. The volume of iron used in making the tube is $$\left( {\pi = \frac{{22}}{7}} \right)$$
Answer & Solution
Correct Answer:
Option
C
External radius R = 4 cm
Internal radius r = 3 cm
Volume of iron used = πR2h - πr2h
= πh(R2 - r2)
= πh(R + r)(R - r)
= $$\frac{{22}}{7}$$ × 20 × (4 + 3) × (4 - 3)
= $$\frac{{22}}{7}$$ × 20 × 7 × 1
= 440 cm3
Internal radius r = 3 cm
Volume of iron used = πR2h - πr2h
= πh(R2 - r2)
= πh(R + r)(R - r)
= $$\frac{{22}}{7}$$ × 20 × (4 + 3) × (4 - 3)
= $$\frac{{22}}{7}$$ × 20 × 7 × 1
= 440 cm3
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