A hollow cylindrical tube 20 cm long is madeofiron andits external and internal diameters are 8 cm and 6 cm respectively. The volume (in cubic cm) of iron used in making the tube is (Take $$ \pi = \frac{22}{7} $$)
volume of hollow cylinder = $$\pi (r1^2 - r2^2) h$$
h = 20
r1 (external radius) =Â Â external diameter$$\div$$2 = 8$$\div$$2 = 4
r2 (internal radius) =Â Â internal diameter $$\div$$2 = 6$$\div$$2 = 3
volume of hollow cylinder = $$\pi (4^2 - 3^2) 20$$=Â $$\frac{22}{7} (7) 20$$ = 440
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