Multiple choice

The SI on a sum of money will be Rs.2500 after 5 years. In the next 5 years Principal is trebled, what will be the total interest at the end of the 10th year?

  1. Rs. 10000

  2. Rs. 11500

  3. Rs. 13420

  4. Rs. 14100

  5. Rs. 15100
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A Correct answer
Explanation

For the first 5 years, SI = Rs. 2500. Let Principal = P and Rate = R%. Then SI = (P × R × 5)/100 = 2500, so P × R = 50000. In the next 5 years, principal becomes 3P. New SI = (3P × R × 5)/100 = 15 × (P × R)/100 = 15 × 50000/100 = Rs. 7500. Total interest after 10 years = 2500 + 7500 = Rs. 10000. The key insight is that SI is directly proportional to principal.

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