If the radius of a sphere decreases by 24%, by what percentage does its total surface area decrease?

Difficulty: Easy

Correct Answer: 42.24%

Explanation:


Introduction / Context:
Area scales as the square of a linear dimension. A decrease in radius reduces surface area by the square of the scale factor.


Given Data / Assumptions:

  • Initial radius r; decreased radius r′ = 0.76 r (since 24% decrease).
  • Surface area S = 4πr^2 and S′ = 4πr′^2.


Concept / Approach:
Compute ratio S′/S = (r′/r)^2 = (0.76)^2 and convert to percent decrease.


Step-by-Step Solution:

S′/S = 0.76^2 = 0.5776Percent decrease = (1 − 0.5776) * 100% = 42.24%


Verification / Alternative check:
Square 76/100 precisely to avoid rounding errors; 76^2 = 5776; move decimal: 0.5776.


Why Other Options Are Wrong:

  • 44%, 49%, 46.2%: Not equal to the exact square-based reduction.


Common Pitfalls:
Subtracting 24% twice or assuming area decreases by exactly double (48%).


Final Answer:
42.24%

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