Well, paying over 40 years they have to pay 0.5% of the total price per month, which is 240% over 480 months.

0.5% of the new price is Cr340,689.6.

That would mean, after 30 years, 60% are left. Which is Cr40,882,800 - however, that is not what they would pay as a lump sum.

[short excursion into financing]

Actually, this sum is 340,689.6 now, 340,689.6 next month, 340,689.6 in two months, and so on, for ten years.

But 340,680.9 next year, or in ten years, isn´t the same as 340,689.6 now. It is the same as the amount you´d have to invest NOW to have 340,689.6 in one year, or in ten years.

That, in turn, depends on the interest rate. At 0%, 340,689.6 now and next year are the same. At 5%, 340,689.6 next year is 340,689.6 divided by 1.05 (1 plus the interest rate), which is about 324,500. 340.689.6 in two years is 340,689.6 divided by 1.05^2 (1.05 times 1.05), or about 309,000. Or general, x/((1+i)^n), with x being the sum, i being the interest rate, and n the number of periods (years, usually) in the future.

This gets more complicated if we include partial interest for months. I´d forget about that, and stick with yearly interest, and use 4,088,280 as a yearly payment. Set an interest rate then - 5% sounds reasonable.

Then, x+(x/((1+i)^1))+(x/((1+i)^2))+...+(x/((1+i)^10)) gets you the lump sum payment for a ship with 10 years of payments left, which you can then use to figure out a new 40-year payment plan.

[/excursion]

I think I have a formula somewhere to figure out what kind of interest rate the "240% over 40 years" payment plan corresponds to. If only I could muster the effort to look for it...