The interest rate of 5.2 here means that the annual interest rate accounts for 5.2% of the principal, and the mortgage of 630,000 yuan has been repaid 200,000 yuan in advance. Then if this 200,000 yuan is not paid back, the annual interest of this 600,000 mortgage is 36,760 yuan. After this 200,000 yuan is paid back, the annual interest is 430,000 yuan, which means that the annual interest is 22,360 yuan, which will be less 10400 yuan per month.