IAS 2 or IFRS 3

During discussion with my fellow regarding Consolidation. I heard something which make me astonished.
My fellow said ” DO YOU KNOW WHEN USING IFRS 3 the PRINCIPLES OF IAS 2 becomes INAPPLICABLE”.

Let me share with you what he was telling me.

Suppose two companies are consolidated.
Parent has an at the cost of inventory of $10.
Subsidiary has an inventory of $15. Due to obsolescence the inventory of Subsidiary has fallen to $12.

Now when consolidated
a) what should be the value of inventory in consolidated accounts?
b) where the loss from obsolescence of inventory has to be reflected in the consolidated accounts.