A solid cylinder of radius 3 cm and height 5 cm is melted to form tiny right circular cones, each with base radius 1 mm and height 1 cm. How many such cones can be made?

Difficulty: Medium

Correct Answer: 13500

Explanation:


Introduction / Context:
Melting and recasting conserves volume. We compute the cylinder volume and divide by the volume of one small cone to find the count of cones produced.


Given Data / Assumptions:

  • Cylinder: r = 3 cm, h = 5 cm → V_cyl = πr^2h.
  • Cone: base radius = 1 mm = 0.1 cm, height = 1 cm → V_cone = (1/3)πr^2h.


Concept / Approach:
Number of cones n = V_cyl / V_cone (volumes in the same units). Convert millimetres to centimetres before substitution.


Step-by-Step Solution:

V_cyl = π * 3^2 * 5 = 45π cm^3V_cone = (1/3)π * (0.1)^2 * 1 = (1/3)π * 0.01 = π/300 cm^3n = 45π / (π/300) = 45 * 300 = 13500


Verification / Alternative check:
π cancels; ensure radius in cm (0.1 cm) to avoid 100× error.


Why Other Options Are Wrong:
They arise from unit mistakes (using 1 mm as 1 cm) or misplacing the 1/3 in cone volume.


Common Pitfalls:
Unit conversion errors; forgetting the 1/3 factor for cone volume; arithmetic slips during division.


Final Answer:
13500

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