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Engineering Exams RRB-JE JE (Junior Engineer) CMA (Chemical and Metallurgical Assistant) DMS (Depot Material Superintendent) CS (Chemical Supervisor - Research) MS (Metallurgical Supervisor - Research) Mathematics 2024 16.12.24 Paper-1 Shift-3 Medium +1 -0.33
If at same rate of interest, in 2 years, the simple interest is ₹56 and compound interest is ₹72, then what is the principal (in ₹)?
Correct Answer: C. 49
Explanation: The correct answer is Option C: 49. To find the principal, we first determine the difference between the compound interest (CI) and simple interest (SI) for the 2-year period. The difference is ₹72 - ₹56 = ₹16. In simple interest, the interest earned each year is equal, so the interest for the first year is ₹56 / 2 = ₹28. The difference of ₹16 between CI and SI in the second year represents the interest earned on the first year's interest. Therefore, the interest rate (R) is (16 / 28) * 100, which simplifies to 400/7%. Finally, using the simple interest formula SI = (P * R * T) / 100, we substitute the known values: 56 = (P * (400/7) * 2) / 100. Solving for P, we get 56 = (P * 800) / 700, which simplifies to 56 = 8P / 7. Multiplying both sides by 7 gives 392 = 8P, and dividing by 8 results in a principal (P) of ₹49.
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