Question

A man deposited Rs.1,000 in a bank. In return he got Rs.1,331. Bank gave interest 10% per annum. How long did he keep the money in the bank?

• A. 5 years
• B. 4 years
• C. 3 years
• D. 1 year

Hint:

Use logarithms to solve for time in compound interest problems when the rate and amount are known.

Answer 1

The Correct Option is A

Step 1: Establish the compound interest formula.
\[ \text{Amount} = \text{Principal} \left(1 + \frac{\text{Rate}}{100}\right)^{\text{Time}} \] Given, \( P = 1000 \), \( R = 10% \), \( A = 1331 \).

Step 2: Solve for time. \[ 1331 = 1000 \left(1 + \frac{10}{100}\right)^t \] \[ 1.331 = (1.1)^t \] \[ t = \log_{1.1}(1.331) \] Approximating or using logarithmic calculations: \[ t \approx 5 \text{ years} \]