If the compound interest for the 3rd and 4th year on a certain principal is Rs.39 and Rs.52 respectively, what is the rate of interest (in %)?

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

Compound interest for the 3rd year = 39

Compound interest for the 4th year = 52

R% = \(\frac{ (CI \; for \; 4th \; year) - (CI \; for \; 3rd \; year) }{(CI \; for \; 3rd \; year)}\)

R% = \(\frac{52 - 39}{39}\) × 100 = 33\(\frac{1}{3}\)%