Hi Safu,
As N Harkawat has explained in his reply, you calculation of total repayment
is wrong in the first place. And this leads you to the value of 13.121%
(which ofcourse is wrong). The total repayment is not 168.75 but it is
140.10 which you can get by using the formula:
= PMT(Interest/12,Term,-Loan)
= PMT((7.75%)/12, 96, -10000)
= 140.10
And now if you use the Rate function you will definitely get back your
original rate:
= RATE(Term,-Total Repyt,Loan)*12
= RATE(96,-140.10,10000)*12
= 7.75%
As N Harkawat has explained, your interest eeps on reducing as the term
starts reducing and the principle amount repaid increases. Your total
repayment remains same at 140.10.
Regards
Mangesh