The actual amount to be repaid after the commercial loan 10 year is the original loan amount plus the loan interest of 10 year, so the total * * * is 700,000 (1+0.005)120, which is correct. However, it should be noted that the calculated value is the value after 10 years. Although the monthly repayment is the same, the time point is not after 10, so the monthly repayment amount should be adjusted to the same time point as that after 10. Since the repayment starts from the month after the loan, the value after the first repayment is changed to 10 year, which is equivalent to X (1+0.005)19, and the value after the second repayment is changed to 10 year, which is equivalent to X (19).

Your algorithm doesn't take into account the influence of time value, but I think it's a bit out of line to do this kind of topic in high school now ... I don't understand, and I'm confused after reading the answer!