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The difference between the outside and the inside surface area of a cylindrical pipe 14 cm long is 44 cm2. the pipe is made of 99 cm3 of metal. If R is the outer radius and r is the inner radius of the pipe, then what is (R + r) equal to? (Take π = 22/7)


1. 9 cm
2. 7.5 cm
3. 6 cm
4. 4.5 cm

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Correct Answer - Option 4 : 4.5 cm

Given:

⇒ Height of cylindrical pipe = 14cm

⇒ Volume of metal used = 99 cm

Formula:

Let r = radius of cylinder and h = height of cylinder

⇒ Volume of cylinder = πr2h

⇒ Curved surface area of cylinder = 2πrh

Calculation:

⇒ 2πRh - 2πrh = 44

⇒ R - r = 0.5cm

Then,

⇒ πR2h - πr2h = 99

⇒ (R2 - r2) = 2.25

⇒ (R + r)(R - r) = 2.25

∴ (R + r) = 4.5

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