Multiple choice

What should be the internal radius of a cylindrical metallic water pipe if the volume of metal used in the pipe is 1,672 cubic units, ensuring an adequate flow rate for the household's water needs, given that the external radius is 1 unit more than the internal radius and the length of the pipe is 28 units?

  1. 4 units

  2. 4.5 units

  3. 8 units

  4. 9 units

  5. 18 units
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Volume of metal = pi * h * (R^2 - r^2) = 1672. Here R = r+1, h=28. So 1672 = (22/7) * 28 * ((r+1)^2 - r^2). 1672 = 88 * (2r+1). 19 = 2r+1, so 2r=18, r=9.

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