Calculation of CSoCI in case of a mid-year acquisition

In the exam paper on June 2006 Parent company Hydan acquired a subsidiary in the middle of the year. Question contents SoCI data pre-acquisition and post-acquisition:
Pre-acquisition Post-acquisition
1 Oct 2005 31 March 2006
Revenue 24 000 35 200
Cost of (18 000) (31 000)
sales
…

In the answer examiner for consolidation purpose used only post-acquisition data but not a difference between post-acquisition and pre-acquisition as we should do in the case of mid-year acquisition.
Why?

Thank you in advance