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A sum of money invested at compound interest amounts in 3 years to ₹ 2,400 and in 4 years to ₹ 2,520. The interest rate per annum is :
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- 5%
- 6%
- 10%
- 12%
Correct Option: A
S.I. on ₹ 2400 for 1 year = ₹ (2,520 – 2,400) = ₹ 120
| ∴ Rate = | % | |
| Principal × Time |
| Rate = | = 5% | |
| 2400 × 1 |
Second Method to solve this question :
Here, b – a = 4 – 3 = 1 and B = Rs 2520, A = ₹ 2400
| R% = |  | − 1 |  | × 100% | |
| A |
| R% = |  | − 1 |  | × 100% | |
| 2400 |
| R% = | | | × 100% | |
| 2400 |
| R% = | × 100% = 5% | |
| 2400 |
