The ratio of the principal amount (P) to the yearly amount (A) is given as 25:28. This means:

P/A = 25/28

To find the yearly rate of interest (R), we can use the formula for simple interest:

Simple Interest (SI) = (P * R * T) / 100

Where: SI = Simple Interest P = Principal amount R = Rate of interest (yearly rate) T = Time (in years)

We are given that the ratio of P to A is 25:28, which means:

P/A = 25/28

So, we can express P in terms of A as:

P = (25/28) * A

Now, let's calculate the simple interest using the given principal and yearly amount:

SI = A - P

Substitute the values of P and A:

SI = A - [(25/28) * A]

To find the rate of interest (R), we need to find the percentage of SI with respect to the principal amount (P):

R = (SI / P) * 100

R = { [A - (25/28) * A] / [(25/28) * A] } * 100

Simplify the expression:

R = { [28A - 25A] / (25A) } * 100

R = (3A / 25A) * 100

R = (3/25) * 100

R = 12%

So, the yearly rate of interest is 12%.