Final answer:
The principle on which the annual interest of Rs 9 is calculated when the annual rate of interest is 6% is the concept of simple interest.
Step-by-step explanation:
The principle on which the annual interest of Rs 9 is calculated when the annual rate of interest is 6% is the concept of simple interest. Simple interest is calculated using the formula:
Interest = Principal * Rate * Time
Here, the Principal is the initial amount, the Rate is the annual interest rate, and the Time is the duration in years. In this case, we have the interest, rate, and need to find the principal:
9 = Principal * 0.06 * 1
To find the principal, we divide both sides of the equation by 0.06:
Principal = 9 / 0.06
Principal = 150
The annual interest of Rs 9 is earned on a principal of Rs 150 when the annual rate of interest is 6%.