The simple interest on a certain sum of money invested at 7.5% per annum for 4 years is ₹243. What was the sum (in ₹) invested?

We need to find the Principal (original amount invested).

Given: Simple Interest = ₹243, Rate = 7.5%, Time = 4 years

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Using the Simple Interest formula:

$SI = \dfrac{P \times R \times T}{100}$

Substituting the known values:

$243 = \dfrac{P \times 7.5 \times 4}{100}$

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Simplifying:

$243 = \dfrac{P \times 30}{100}$

$243 = \dfrac{30P}{100}$

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Solving for P:

$243 \times 100 = 30P$

$24,300 = 30P$

$P = \dfrac{24,300}{30}$

$P = 810$

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Verification:

$SI = \dfrac{810 \times 7.5 \times 4}{100} = \dfrac{24,300}{100} = 243$ ✓

The sum invested was ₹810.