Adjustment to profit

Hello,

I have this question taken from the BPP revision kit paper reference 17.11 which goes:

The accountant at investotech discovered the following errors after calculating the company’s profit for 20×3:

1. a non-current asset costing $50,000 has been included in the purchases account.
2. stationery costing $10,000 has been included as closing inventory of raw materials, instead of stationery expenses.

What is the effect of these errors on gross profit and net profit for the year?

My answer was an understatement of gross profit by $60,000 and an understatement of net profit of $50,000 which is incorrect according to the answers on BPP.

The answer according to the BPP kit is: GP understated by $40,000 and NP understated by $30,000.

My thinking is this; the first one of $50,000 is straight forward. However, i can’t seem to get my head round the second one. My point of view and questions are:

1. $10,000 of stationery is in closing inventory. in order to remove this, the double entry would be to debit the closing inventory which would decrease closing inventory, which in turn will decrease gross profit meaning there is an overstatement of $10,000 on GP. And that’s fine, because the $50,000 understatement of the first error then has $10,000 of the overstatement offset against it which seems to agree with part of BPP’s answer. Where i’m struggling is with the other side of the journal. It seems that to debit the closing inventory of the said amount, i then need to credit an account. Stationery is the account with an amount omitted, but crediting it just wouldn’t make sense. This would increase the NP.

My second observation was this:
If the $10,000 is in closing inventory; could it be that it is a debit balance in itself that is a part of an account that is larger than the $10,000, so in order to remove it, i then credit the closing inventory and debit stationery expenses, which would make more sense as the other side of the journal would debit the stationery expenses account and therefore the net profit is reduced. However, the GP would again be understated by the $10,000 and adding it to the $50,000 would make an understatement of $60,000 of GP and an understatement of $50,000 NP. This is my logic and thinking behind it. I just can’t understand why NP would be understated by $30,000. It’s like the $10,000 error is hitting the NP twice?

Many thanks and apologies for the in-depth question. I am trying to be very ‘economical’ with any questions that really do need posting and seeing if i can find understanding through the answers BPP provide.