(8500-4500)X0.2+(4500-1500)X0.1+1500x0.03=1145
500x(0.1+1)=550 500x(0.1+1)^3=665.5
y(0)=60000 r=1%,n=25*12; x=每月还的钱,y（n)=第几个月还欠银行的钱所以y1=( y(0)*r+y(0))-x; y2=[（y(0)*r +y(0))-x ]*r+[y(0)*r+y(0)-x]-x; y3= {[（y(0)*r +y(0))-x ]*r+[y(0)*r+y(0)-x]-x} *r+{[（y(0)*r +y(0))-x ]*r+[y(0)*r+y(0)-x]-x}-x}以此类推y4=y3*r+y3-x;一直到y(25*12) =0 这个规律 x=y（0）*r*（1+r）^n/(1+r)^n-1 计算结果
每月还钱=631.93