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# A hollow cylindrical pipe is 56 cm long. Its outer and inner radii are 20 cm and 16 cm respectively. Find the volume of the iron used in making the pipe.

Answer :

**Concept Used:** Volume of the iron used = External volume – Internal volume

Volume of Cylinder = πr^{2}h

Where r = radius of the cylinder and h = height of the cylinder.

**Given:** Outer Radii = 20 cm

Inner radii = 16 cm

Height of pipe = 56 cm

**Assumption:** Let r_{1} be the radius of the inner cylindrical portion and r_{2} be the radius of the outer cylindrical portion. And h be the height of Cylinder.

**Explanation:**

Volume of iron Used = πr_{1}^{2}h^{2} – πr_{2}^{2}h^{2}

Volume of Iron Used = πh(r_{1}^{2} – r_{2}^{2} )

The volume of Iron Used

The volume of Iron Used = [22 × 8 × (400 – 256)] cm^{3}

The volume of Iron Used = [22 × 8 × 44] cm^{3}

The volume of Iron Used = 7744 cm^{3}

**Hence, The volume of the Iron Used is 7744 cm ^{3}.**

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