Discussion

If Rs.450 amount to Rs.540 in 4 years, what will it amount to in 6 years at the same rate % per annum?

Answer: C

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

Find the rate from the four-year figure.

\[ \text{SI} = 540 - 450 = 90 \quad\Longrightarrow\quad 90 = \frac{450 \times R \times 4}{100} = 18R \]

\[ R = 5\% \]

\[ \text{SI over 6 years} = \frac{450 \times 5 \times 6}{100} = 135 \quad\Longrightarrow\quad \text{amount} = \text{Rs. } 585 \]

Since simple interest is linear in time, the shortcut is \( 90 \times \tfrac{6}{4} = 135 \).

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