Matching principal and interest method: loan principal: 420,000 yuan, assuming annual interest rate: 4.900%, loan life:15; Monthly repayment of principal and interest: 3299.5 yuan, total repayment of principal and interest: 5939 10 yuan, * * interest payable: 178. The interest paid in 1 month is:1715; The first 1 month principal repayment is:1584.5; Since then, the monthly interest repayment amount has decreased and the principal has increased. (without considering the adjustment of interest rate in the middle)