In past paper June 2009 Q5 required (a), when calculating IRR, the answer said that IRR cannot be calculated on proportions of projects and it must be calculated on the NPV of full projects. Can somebody tell me why?
Arithmetically it can be calculated, but what the examiner means is that we could not really use the IRR’s because it is not valid to compare an IRR of (say) 20% with an IRR of (say) 25% if the 25% was only on a small amount.