Trial balance to Statement of P or Loss F3 ACCA June 2014

Hi John,

The following question on SOPL:

Keswick Co acquired 80% of the share capital of Derwent Co on 1 June 20X5. The summarised draft statements of profit or loss for Keswick Co and Derwent Co for the year ended 31 May 20X6 are shown below:
Keswick Co Derwent Co
$000 $000
Revenue 8,400 3,200
Cost of sales (4,600) (1,700)
–––––– ––––––
Gross profit 3,800 1,500
Operating expenses (2,200) (960)
–––––– ––––––
Profit before tax 1,600 540
Tax (600) (140)
–––––– ––––––
Profit for the year 1,000 400
–––––– ––––––
Added info:

During the year Keswick Co sold goods costing $1,000,000 to Derwent Co for $1,500,000. At 31 May 20X6, 30%of these goods remained in Derwent Co’s inventory.
My Question: How do I apply the 30% (if applicable anywhere)?
My workings:
Revenue 8,400 + 3,200 – 1500 still in Sub’s inventory = 10,100
Cost of sales (4,600) +(1,700×0.2) = ? I get 4940 and not 4950
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Gross profit 3,800 +1,500 = ? I got 5160 and not 5150
Operating expenses (2,200) +(960) = 3160
–––––– ––––––
Profit before tax 1,600 +540 = 2000 and not 1990 (noted $10 error carrying over)
Tax (600) +(140) = 740 (noted $10 error carrying over)
–––––– ––––––
Profit for the year 1,000 +400 = 1260 and not 1250 (noted $10 error carrying over)

Why is there a $10 variance? Have I miscalculated somewhere?
And how is the 30% applied in the above? I’m not sure if it is relevant to note or not.
🙂