Cone scaled in radius and height — new volume ratio: The base radius and height of a cone are both doubled. What is the ratio of the new volume to the original volume?
Aptitude
Volume and Surface Area
Difficulty: Easy
Choose an option
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A8 : 7
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B8 : 3
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C8 : 1
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D8 : 5
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ENone of these
Answer
Correct Answer: 8 : 1
Explanation
Introduction / Context:Volume of a cone is V = (1/3)πr^2h. Scaling r and h scales volume by r^2h, i.e., by the square of radius scale times the height scale.
Given Data / Assumptions:r → 2r and h → 2h.
Concept / Approach:New/old volume factor = (2^2) * (2) = 8.
Step-by-Step Solution:V_new / V_old = (r_new^2 h_new)/(r^2 h) = (4r^2 * 2h)/(r^2 h) = 8
Verification / Alternative check:Pick numbers (e.g., r=1, h=1) to see old V=(1/3)π, new V=(8/3)π → ratio 8:1.
Why Other Options Are Wrong:Other ratios ignore the quadratic dependence on radius and the linear dependence on height.
Common Pitfalls:Adding scale factors instead of multiplying; forgetting radius is squared in volume.
Final Answer:8 : 1