Difficulty: Hard
Correct Answer: Data is not sufficient
Explanation:
Introduction:
This question checks whether the given changes in rate and time provide enough information to uniquely determine the principal under simple interest. Simple interest depends on three variables: principal P, rate r, and time t. If the problem only gives information about how interest changes when r or t changes, we must see if those constraints uniquely identify P, or if multiple combinations of P, r, and t can satisfy them.
Given Data / Assumptions:
Concept / Approach:
Translate each “increase” into an equation. A 2% increase in rate changes SI by (P * 2 * t)/100. A 2-year increase in time changes SI by (P * r * 2)/100. These produce relationships involving P*t and P*r, but do not directly give P alone unless we can also relate r and t uniquely.
Step-by-Step Solution:
Rate increase condition: (P * 2 * t) / 100 = 108
So P * t = 108 * 100 / 2 = 5400
Time increase condition: (P * r * 2) / 100 = 180
So P * r = 180 * 100 / 2 = 9000
We now know P*t and P*r, but we do not know r or t individually.
Many pairs (r, t) can satisfy these while giving different P values.
Verification / Alternative check:
Example 1: If t = 6 years, then P = 5400/6 = 900, and r = 9000/900 = 10%. Example 2: If t = 9 years, then P = 5400/9 = 600, and r = 9000/600 = 15%. Both satisfy the given increases, but P is different. Hence P is not uniquely determined.
Why Other Options Are Wrong:
₹540, ₹415, ₹404, and ₹450 are specific values, but the information allows multiple valid principals, so no single number can be confirmed as the only answer.
Common Pitfalls:
Assuming the original rate or time is implicitly known, or trying to compute SI without enough independent equations. Another mistake is to treat “increase by 2%” as “multiply by 1.02” (that would be a different interpretation than 2 percentage points).
Final Answer:
Data is not sufficient to uniquely determine the principal.
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