How did you get 125/100

When you have a percentage $R$, you convert it to a decimal by dividing by 100:

$$\frac{R}{100} = \frac{25}{100} = 0.25$$

Then, in the formula, we add 1 to this decimal:

$$1 + \frac{25}{100} = 1 + 0.25 = 1.25$$

To express 1.25 as a fraction, we can write it as:

$$1.25 = \frac{125}{100}$$

This is how we arrive at $\frac{125}{100}$ in the compound interest calculation.