Solution:

Given, the amount will be 9 times its principle in 2 years.

Let the principle be P.

After 2 years, the amount will be 9P.

Let the rate of interest be R.

Let the interest be I.

Formula:

The formula to calculate compound interest is given by:

A = P(1 + R/100)^n

Where,

A = Amount
P = Principle
R = Rate of Interest
n = Time period

We need to find the value of R.

Calculation:

After 2 years, the amount will be 9P.

So, using the formula of compound interest:

9P = P(1 + R/100)^2

Taking square root on both sides, we get:

3 = (1 + R/100)

R/100 = 3 - 1

R/100 = 2

R = 2 x 100

R = 200%

Therefore, the compound rate of interest is 200%.

Explanation:

Compound interest is the interest calculated on the principal amount as well as the accumulated interest. It is different from simple interest, where the interest is calculated only on the principal amount.

In this problem, we are given that the amount will be 9 times the principal amount after 2 years. We need to find the compound rate of interest.

We use the formula of compound interest to calculate the rate of interest. We substitute the given values in the formula and solve for the rate of interest.

The calculation shows that the compound rate of interest is 200%.

This means that the amount will be 9 times the principal amount after 2 years if the interest is compounded at the rate of 200% per annum.