If the ratio of principal and amount in the current year at a simple rate of interest is 9:17 and after 24 years this ratio will become 15:43. Find the rate of interest.

4.07%

                         P  :   A                   ⇒       P  :  A

                        ( 9   :   17) × 15              135  : 255   

after 24 years    (15  :    43) × 9               135  :  387

387 - 255 = 132 ( in 24 years)

SI in 1 year = \(\frac{132}{24}\) = 5.5

Rate = \(\frac{5.5}{135}\) × 100 % = 4.07%