Partial Disposal – Group gain/loss versus parent gain/loss computation

Hello,

I am slightly confused when diposing of a subsidiary (i.e. subsidiary to associate). Why do you need to calculate the effect on the seperate financial statements of the parent and the group profit/loss on disposal also?

Can you not simply calculate the group profit on disposal and deduct this from consolidated retained earnings. Is there some kind of reconcilation someone can provide to properly understand these two computations, when they are both required and the associated double entries. I have looked at the lectures and the book but it is not entirely clear!

thanks