Comparing compound interest rates (Half-yearly vs Annually)
Question
A principal P becomes Q in 1 year when compounded half-yearly with R% annual rate of interest. If the same principal P becomes Q in 1 year when compounded annually with S% annual rate of interest, then which one of the following is correct?
Options
R = S
R > S
R < S
R ≤ S
Explanation
Write out the compound interest equations for a 1-year timeline under both scenarios[cite: 3744, 3745]:
Q = P \left(1 + R/200\right)²
Q = P \left(1 + S/100\right)^1
Since the final amount Q and initial principal P are identical in both cases, equate the multipliers [cite: 3744, 3745]: \left(1 + R/200\right)² = 1 + S/100 1 + R/100 + R²/40000 = 1 + S/100 R/100 + R²/40000 = S/100
Because the term ⟨MATH⟩R²/40000⟨/MATH⟩ is strictly positive, it follows that ⟨MATH⟩S/100⟨/MATH⟩ must be strictly greater than ⟨MATH⟩R/100⟨/MATH⟩. This forces S > R, which can be rewritten as R < S.
Answer: (c).
Question details
Year
2023
Paper
CSAT
Question
Q44
Section
Data Interpretation & Sufficiency
Sub-topic
Comparative Quantitative
Type
Comparative quantitative
Difficulty
Easy
Source hint
Quantitative comparison
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