Transfer disposal account question

On page 35, 36 problem 7.9 and 7.10 on ACCA practice and revision kit paper F3 BPP
we have following ”
Plant and machinery- cost on 30 september 20X3
On Debit side
20X2
1 Oct Balance 200,000
20X3
1 Apr Cash-purchase of plant 50,000
Total 250,000
On credit side
20X3
30 Jun Transfer disposal account 40,000
30 Sep Balance 210,000
Total 250,000
The question ask to count the depreciation charge for plant and machinery with the depreciation rate is 20% per year on cost, with proportional depreciation for items purchased or sold during the year.
The answer given that
Plant held all year (200,000-40,000) *20% =32,000
Disposal =40,000*20%*9/12= 6000
Addition 50,000*20%*6/12= 5000
In total 43,000
But in the question the Transfer disposal account 40,000 only begin at 1 Oct, why the answer given the plant held all year?