All-Current COGS mock exam vs Schweser

Ok im confused… in the mock exam moringn session (q 24), they just translate cogs at average rate which is normally ok. But i assumed that because we had begging inv. and ending inv. numbers, we needed to calclate purchases===then translate such as: Cogs= Beg inv + purch- end = 100 (translated at historical rate of year end 2007 inv) + 800 (at average) - 200 (average) In scheser Qbank this is how they do it when you are given beg and end inv numbers… what do you guys reckon?

explanation @ http://www.analystforum.com/phorums/read.php?12,957350,957373

im such an idiot…i forgot the other question was temporal and this one is current… i still got the right answer as the change was negligable… thanks