Final answer:
To find the rate of interest when the simple interest is 30% of the principal over 5 years, we use the simple interest formula. By substituting the respective values, we find that the rate of interest is 6% per annum.
Step-by-step explanation:
The question asks to find the rate of interest when the simple interest earned on a certain sum in 5 years is 30% of the sum. Simple interest (SI) is calculated using the formula SI = PRT/100, where P is the principal amount, R is the rate of interest per annum, and T is the time in years.
To find the rate of interest, we can rearrange the formula to R = (SI * 100) / (P * T). Given that SI is 30% of the principal P, and T is 5 years, we substitute these values into the formula: R = (0.30 * P * 100) / (P * 5). Simplifying this, we find that R = (30 * 100) / 5, which results in R = 600 / 5. Thus, R = 6%.
Therefore, the rate of interest is 6% per annum.