F5 Dec 2009 (Secure Net) Q1 part (b)

Dear Sir,

I’ve found the above mentioned question very tricky as I tackled it in following way:

PRICE VAR
Actual Quantity used x Difference in price of Material
3500kg x $1.25 = 4375 (A)

Price Planning Var
3500kg x $4.8-$4 = 2800(A)
Price Operational Var
3500kg x $5.25- $4.8 = 1575 (A)

USAGE VAR
Difference in original std Vs Actual Usage x Std price/kg
4000kg-3500kg x $4 = 2000(F)
Usage Planning Var
4200kg-4000kg x $4 = 800(A)
Usage Operational Var
4200kg – 3500kg x $4 = 2800(F)

The above planning and operational variances check perfectly with basic price and usage variances and the basic variances check with the total Variance.

I can see that the examiner has done it differently. Would I have got any marks if I’d done it this way?
I can see, looking at the answer in the BPP revision kit as to what they’ve done. But there is no way I could’ve done that If I hadn’t looked at the answer.
How can I practice for this kind of a confusing question? What fundamental principle or rule needs to be understood?

Your clarification would be much appriciated.

Thanks,

Bhupinder