Shankar borrowed Rs. 7,200 at simple interest and repaid an amount of Rs. 9,504 after 7 years. If the interest rate p.a charged for first 4 years was 5%, find the interest rate p.a. charged for the last 3 years.
S.I. = 9,504 – 7,200 = Rs. 2,304 ⟹(7200 × 4 × 5)/100 + (7200 × 3 × R)/100 = 2,304 ⟹ 1440 + 216 R = 2,304⟹ R = 4% p.a.