A sum triple itself in 9 years at simple interest. Find the rate of interest per annum is.

To solve this problem, we'll use the formula for simple interest.

The formula is as follows:

Simple Interest (SI) = (Principal (P) × Rate (R) × Time (T)) / 100

Calculation:

SI = 2 × P

We are given the time (T) as 9 years.

We need to find the rate (R) per annum.

⇒ 2 × P = (P × R × 9) / 100

Now, we need to solve for R:

⇒ 2 × P = (9 × P × R) / 100

Divide both sides by P:

⇒ 2 = (9 × R) / 100

Now, multiply both sides by 100:

⇒ 200 = 9 × R

Finally, divide both sides by 9:

⇒ R = 200 / 9
⇒ R = 

Hence, the rate of interest per annum is approximately .

Mistake Points

If a sum triples itself in 9 years using simple interest, this means that the amount of interest earned over those 9 years is twice the original sum.

i.e. When the Principal is P, then Interest will be 2P.