Do you really mean 1991? If so, I'm afraid I don't have that question to hand, I'd have to have a good hunt around, unless you can give me an idea of what it was asking?
But let me have a go at answering anyway, to see whether this helps:
For pricing, you need to put all past premium data (and claims of course) onto an 'as-if' basis, ie as if you were selling the business when you'll be planning to. This means taking past premiums and adjusting for the historic rate changes so that you get an idea of what you would bring in if you sold the business today (or whenever you'll be selling it).
Lots of ways of doing this, although the method should result in an identical answer - you could either just increase all the old premiums by the historical rate changes, compounding up (as in Darren's reply above), which to me is the easiest way of understanding it. OR - you could create an 'index', which is effectively the multiplier you use to apply to each historic premium (in other words, each index value is the compounded figures). OR - you could create another 'index', which you divide into the premium. Really, that index would just be like the reciprocal of the multiplier index of course. Maybe that's what you've done differently for the two questions? But you should find that you get the right (same) answer either way, as long as you've divided or multiplied (and compounded) correctly.
Hope this makes sense!
