The interest rate is 30 yuan per month on 10,000 yuan. The monthly interest rate = 30/100/100=0.3. That is to say, if the interest rate is 30 yuan per month on 10,000 yuan, the monthly interest rate is 0.3. The interest rate is generally expressed in hundreds. It is expressed in parts, so the calculation of the interest rate above requires dividing 30 parts per 10,000 by 100. If you want to calculate the annual interest, just multiply it by twelve months, so the annual interest = 0.3?12=3.6