Calculate the annual interest rate given the principal amount, simple interest earned, and time period.

The principal amount is $P = \text{N}20,000$.
The simple interest earned is $I = \text{N}2,500$.
The time period is $T = 3$ years.

The formula for simple interest is:

where $I$ is the interest, $P$ is the principal, $R$ is the annual interest rate (as a decimal), and $T$ is the time in years.

To express the rate as a percentage, multiply by 100.

The interest rate is approximately 4.17%.