Percy Byron practice question on ROE differences under Equity, Consolidation with Partial/Full Goodwill methods

I can’t get the answer behind this practice question in EcoLearning System. It is about whether ROE will be the same for the acquirer’s ROE (where Equity = Beg.Equity i.e. at the acquisition date)
NimMount Plc acquired 50% of Boswell for $320m. Net Assets of Boswell at FV was $580m.
NI for NimMount 75, Boswell 10
Beg. Equity for NimMount 1,430
I am puzzled by the right answer which says ROE would be the same for either consolidation method but different under Equity. The logic is explained as this : NI would be the same, but Equity would be higher under either consolidation by NCI of $320m.
But If I remember correctly, NCI will be different under full vs partial goodwill:
NCI(full goodwill)= 50% of 640m (FV of Boswell implied from purchase price) = $320m
NCI(part.goodwill)= 50% of 580m (FV of Net Assets of Boswell at the acquisition)= $290m
What am I missing here or perhaps answer for this practice question is WRONG?