Change in ownership structure

I have been solving a group question and I realised that in the calculation of the movement in equity ,where a parent holding 60% of interest from beginning of period till end of the period when it acquired further 20%, the NCI’s share of the impairment of goodwill ,calculated using full goodwill method, was not deducted from the carrying amount of the NCI before computing the proportion disposed.
Could you help me on that?