The simple interest on a certain sum for 2 yr is ₹

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The simple interest on a certain sum for 2 yr is ₹ 120 and compound interest is ₹ 129. Find the rate of interest.

1. 14%
2. 15%
3. 12%
4. none of the above

Correct Option: B

Here, n = 2 yr, SI = ₹ 120 and CI = ₹ 129
CI = SI (1+ R/200)
⇒ 129 = 120(1 + R/200)
⇒ 129/120 = 1 + R/200
⇒ (129/120) - 1 = R / 200
⇒ 9/120 = R/200
∴ R = (9 x 200)/120 = 15%