Discussion

A certain sum amounts to Rs.1725 in 3 years and Rs.1875 in 5 years. Find the rate % per annum?

Answer: B

\[ \text{SI} = \frac{P \times R \times T}{100} \]

Under simple interest the yearly addition is constant, so the gap between the two amounts covers two years.

\[ 1875 - 1725 = 150 \text{ over 2 years} \quad\Longrightarrow\quad 75 \text{ per year} \]

\[ P = 1725 - 3 \times 75 = \text{Rs. } 1500 \]

\[ R = \frac{75 \times 100}{1500} = 5\% \]

Working back three years from the first amount recovers the principal.

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