Discussion

A sum of money deposited at C.I. amounts to Rs.2420 in 2 years and to Rs.2662 in 3 years. Find the rate percent?

Answer: B

\[ A = P\left(1 + \frac{R}{100}\right)^{n}, \qquad \text{CI} = A - P, \qquad \text{SI} = \frac{PRn}{100} \]

The step from year 2 to year 3 is one year's growth.

\[ 1 + \frac{R}{100} = \frac{2662}{2420} = 1.1 \]

\[ R = 10\% \]

Equivalently, the Rs. 242 earned in the third year is 10% of the Rs. 2420 standing at its start. Neither the principal nor the total time is needed.

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