A hollow cylinder with outer radius 4 cm and height 2 cm is made up of 1 cm thick metal sheet. What is the volume of metal used? (Take $$\pi=\frac{22}{7}$$)
Outer radius of cylinder = 4 cm
Thickness = 1 cm
Then, Inner radius = 3 cm
Height = 2 cm
Then, Volume of the metal = $$\pi (R^2 - r^2) h$$ where R = Outer radius, r = Inner radius and h = Height.
Volume = $$\dfrac{22}{7}\times(4^2 - 3^2)\times2$$
$$= \dfrac{22}{7}\times7\times1\times2$$Â Â Â Â ($$\because (a^2 - b^2) = (a+b)(a-b)$$)
$$= 44 cm^2$$
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