Bad debts – BPP 11.11

At Jan 20×1, there was an allowance for receivables of $3,000. During the year. $1,000 of debts were written off as irrecoverable, and $800 of debts previously written off recovered. At 31 December 20×1, it was decided to adjust the allowance for receivables to 5% of receivables which are $20,000.

The answer is 1,800. I got 1,850

I calculate:
New allowance: (20,000-1,000) x 5%=950
Decrease in allowance =2050
Irr debts =1000
Debts prev written off =800
Total expense (2,050-1,000+800) =1,850

Where am I making an error?

Thanks