A certain sum of money becomes Rs. 81000 in 4 years and it becomes Rs. 89373 in 7 years. Find the rate of interest p.a., if compounded annually.

3\(\frac{1}{3}\)%

Amt₇ = Amt₃ (1 + \(\frac{R}{100}\))^t

ATQ,

⇒ 89373 = 81000 (1 + \(\frac{R}{100}\))³

⇒ 29791 = 27000 (1 + \(\frac{R}{100}\))³

⇒ \(\frac{29791}{27000}\) = (1 + \(\frac{R}{100}\))³

⇒ (\(\frac{31}{30}\))³ = (1 + \(\frac{R}{100}\))³

⇒ \(\frac{31}{30}\) = (1 + \(\frac{R}{100}\))

⇒  R = \(\frac{100}{30}\) = 3\(\frac{1}{3}\)%