✔ 最佳答案
The monthly interest rate r = 7.5%/12 = 0.00625
The balance amount after 1 month
= 280000 * (1 + r) - 1957.8
The balance amount after 2 months
= [280000 * (1 + r) - 1957.8](1 + r) - 1957.8
= 280000 * (1 + r)^2 - [1957.8(1 + r) + 1957.8]
The balance amount after 3 months
= [280000 * (1 + r)^2 - [1957.8(1 + r) + 1957.8]](1 + r) - 1957.8
= 280000 * (1 + r)^3 - [1957.8(1 + r)^2 + 1957.8(1 + r) + 1957.8]
= 280000 * (1 + r)^3 - 1957.8[(1 + r)^3 - 1]/r
The balance amount after 7 years (84 months)
= 280000 * (1 + r)^84 - 1957.8[(1 + r)^84) - 1]/r
= 472555.77 - 215420.40
= 257135.37