I don't think that is right.
In your case, tha rate of increase from .8 to .9 is not the same (it is greater) as the increase from .9 to 1.0.
Therefore, the increase can't be a constant number, but rather a constant rate.
Not that I know how to solve this, but I don't think that is right...unless of course the problem is worded incorrectly.
Nimit, can you double check the wording, or perhaps provide answer choices?