Q.Divide ₹21,866 into two parts such that the compound amount of the first part for 3 years is equal to the compound amount of the second part for 5 years, at an annual compound interest rate of 5%.

Let the amount of the first part be \(x\) rupees and the second part be \((21866 - x)\) rupees. \(\therefore\) Compound amount of ₹\(x\) for 3 years at 5% annual interest \(= x\left(1 + \cfrac{5}{100}\right)^3 = x\left(\cfrac{21}{20}\right)^3\) Compound amount of ₹\((21866 - x)\) for 5 years at 5% annual interest \(= (21866 - x)\left(1 + \cfrac{5}{100}\right)^5 = (21866 - x)\left(\cfrac{21}{20}\right)^5\) As per the question: \(x\left(\cfrac{21}{20}\right)^3 = (21866 - x)\left(\cfrac{21}{20}\right)^5\) ⇒ \(x = (21866 - x)\left(\cfrac{21}{20}\right)^2 = (21866 - x) \times \cfrac{441}{400}\) ⇒ \(400x = 441(21866 - x)\) ⇒ \(400x + 441x = 441 \times 21866\) ⇒ \(841x = 441 \times 21866\) ⇒ \(x = \cfrac{441 \times 26}{1} = 11466\) \(\therefore\) First part = ₹11,466 and second part = ₹\(21866 - 11466 = 10400\) So, the two parts are ₹11,466 and ₹10,400 respectively.
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