Compound Interest : Future Value and Present Value
posted by Math .
Payments of $1800 and $2400 weere made on a $10,000 variablerate loan 18 and 30 months after the date of the loan. The interest rate was 11.5% compounded semiannually for the first two years and 10.74% compounded monthly thereafter. What amount was owed on the loan after three years?

make a 'timegraph' and label points 0,(now), 18,24 (the rate changes here), 30, and 36.
place 10000 at 0
1800 at 18 and 2400 at 30
you want to bring all three money values up to timepoint 36
the 1800 is charged a rate of .115/12 for 6 months and then .1074/12 for the next 12 months.
its value at 36 = 1800(1+.115/12)^6(1+.1074/12)^12
= $2121.10
the 2400 is charged .1074/12 for 6 months
its value is 2400(1+.1074/12)^6
= $2531.80
The original debt at 36 has a value of
10000(1+.115/12)^24(1+.1074/12)^12
= 13990.97
so the amount owing is
13990.97  2531.80  2121.10
= 9338.07
(please check my arithmetic)