Difficulty: Medium
Correct Answer: $13,841.89
Explanation:
Introduction / Context:
This question is a present value problem under compound interest. We know the future value (amount) after compounding annually, and we must find the initial principal. The compound amount formula is A = P * (1 + r/100)^t. Rearranging gives P = A / (1 + r/100)^t. This is a standard financial math concept: discounting a future amount back to today using the compound growth factor.
Given Data / Assumptions:
Concept / Approach:
Rearrange compound interest formula to find present value:
P = A / (1 + r/100)^t
Here, growth factor = (1.03)^20.
Step-by-Step Solution:
A = 25000
r = 3%, so (1 + r/100) = 1.03
t = 20
P = 25000 / (1.03^20)
1.03^20 ≈ 1.8061
P ≈ 25000 / 1.8061 ≈ 13841.89
Principal ≈ $13,841.89
Verification / Alternative check:
If P ≈ 13841.89, then A = 13841.89 * (1.03^20). Since 1.03^20 ≈ 1.8061, the amount becomes approximately 13841.89*1.8061 ≈ 25000, confirming correctness (small differences occur due to rounding during intermediate steps).
Why Other Options Are Wrong:
$15,625 corresponds to simple interest growth of 60% (1.6 factor), not compounding. $14,821 and $13,468 result from incorrect power/rounding or wrong compounding period. $57,389 is not a present value; it is larger than the future amount, so it cannot be correct.
Common Pitfalls:
Using simple interest instead of compounding, using t = 20 months instead of 20 years, or forgetting to divide by the compound factor and instead multiplying.
Final Answer:
The required principal is approximately $13,841.89.
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