exam question – receivables

– receivables at 1 Jan 2013 is $10,000
– receivables at 31 Dec 2013 is $9,000
– total receipts during 2013 (including cash sales of $5,000 was $85,000

Q> what is the sales revenue figure for 2013?

My question: why is the cash receipt (from trade receivables so credit sales) recorded as $85,000 and not $80,000 ($85,000 – $5,000)?

surely the cash sales should not be part of the credit sales?

kind regards,