Let us say you buy have an Asset class with a bunch of things and they initially cost 80000 on January 1 2013. There is no residual value but the useful life of this asset class is 8 years and it is being depreciated using straight line method. It is now january 1 2015 and you buy another thing to add to this asset class worth 12000. You also believe the remaining useful life of this asset class is 5 years now. When calculating depreciation for this new item, what do you use as useful life. Will it be 8 years or 5 years?