Height ratio for equal volumes (cylinder vs cone): A right cylinder and a right circular cone have the same radius and the same volume. Find the ratio of the height of the cylinder to the height of the cone.

Difficulty: Easy

Correct Answer: 1 : 3

Explanation:


Introduction / Context:
With the same radius, equal volumes force a relationship between heights using V_cyl = π r^2 h_c and V_cone = (1/3) π r^2 h_k. Equate and solve for h_c : h_k.


Given Data / Assumptions:

  • Same radius r; equal volumes.
  • V_cyl = π r^2 h_c, V_cone = (1/3) π r^2 h_k.


Concept / Approach:

  • Set π r^2 h_c = (1/3) π r^2 h_k ⇒ h_c = h_k / 3.


Step-by-Step Solution:

h_c = (1/3) h_k ⇒ h_c : h_k = 1 : 3.


Verification / Alternative check:

Pick r=1, h_k=3: V_cone=(1/3)π*1*3=π; with h_c=1, V_cyl=π.


Why Other Options Are Wrong:

  • 3:1 / 3:5 / 2:5: Inconsistent with the cone’s 1/3 volume factor.


Common Pitfalls:

  • Inverting the ratio (writing 3:1 rather than 1:3).


Final Answer:

1 : 3

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