Given: The simple interest at R % p.a. on a certain principal P is (
9
16
)th of P and R is equal to the number of years (N). Formula Used: Simple interest = (Principal × time × rate)/100 Calculation: ⇒ 9P/16 = P × N × N/100 ⇒ N2 = 900/16 ⇒ N = 30/4 = 7.5 years ∴ required number of years = 7.5 years