With a given rate of simple interest, the ratio of principal and amount for a certain period of time is 3 : 4 . After 2 years, with the same rate of interest, the ratio of the principal and amount becomes 5 : 6 . The rate of interest is?

 6\(\frac{2}{3}\)%

             P  :   A                     ⇒       P  :  A

               3 : 4     after 2 years        5 : 6 

Since P remains same

               15: 20                            15 : 18

20 - 18 = 2 ( in 2 years)

SI in 1 year = \(\frac{2}{2}\) = 1

Rate = \(\frac{1}{15}\) × 100 % = 6\(\frac{2}{3}\)%