Adjustment to equity

Hi

I wonder if someone can help me?

I am calculating adjustments to parents equity where you have
Cost/paid amount x
NCI. x
= Adj to parents equity x

When calculating the NCI element I am taking the net assets and times this by % brought/sold then dividing it by the original NCI percentage, however in some questions I have done this is not the case, the NCI element is being calculated by net assets x original NCI percentage. I am struggling to understand the difference is someone able to explain this to me?

Example
JL acquired 80% of DP then sold 25% half way through the year, NCI is measured at proportionate share of net assets
Answer
Cost of 25% 4400
NCI 3780 (18900 x 20%) this is the bit I don't understand!
Adj to parent equity 620

Example 2
Blt acquired 60% then acquired a further 20% half way through the year, NCI equity at acq 127000, NCI is measured at proportionate share of net assets, 30000 profit was made during the year
Cost 135000
NCI 66500 (127000 + (30000 / 12 x 6) x 20% / 40%
Adj to parent 68500

My question is why is the NCI calculated differently from example 1 and 2?

Please help so confused

Thanks