Financial Maths question - Calculate number of years over which loan will be repaid A loan has to be repaid over 3n years, through annual repayment installments of 5000 each at an annual interest rate of 10%. Sum of the Interests paid in the (n+1) and that in the 2n+1 year is 5000.
calculate the number of years over which the loan is to be repaid. 
I normally use the present value or future value formula, unsure how to use those formulas in this situation, as I dont have a value for the debt.
any help appreciated. 

If $P(n)$ is the amount due at the end of year $n$, and assuming payment at the end of the year you have
$$
P(n+1) = P(n) + 0.1 P(n) -5000
$$
If the payment is made at the start of the year than use
$$
P(n+1) = 1.1 (P(n)-5000
$$
Also total interest paid up to and including year n is
$$
I(n+1) = I(n) + 0.1 P(n)
$$
$P(0)$ is the initial principal and $I(0)=0$ and $P(3n)=0$.
First show that 
$$P(n) = A (1.1)^n + B $$
and 
$$I(n) = C \cdot n + D (1.1)^n + E$$
