2021 · Q34
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)
Elementary MathematicsMensuration
- A9 cm
- B7.5 cm
- C6 cm
- D4.5 cm
Explanation
The lateral-area difference is 2πh(R−r) = 44 with h = 14, so R − r = 44/(2π·14) = 0.5. The metal volume is πh(R²−r²) = 99, i.e. 44·0.5·(R+r) = 99, giving R + r = 4.5 cm. Hence option D.