They COULD have gotten $1,800, if they had paid all their A/P invoices within the discount period.  But they blew it.  They mailed some of their payments after the discount period expired, so they had to pay full price for a bunch of stuff, and only qualified for $800 of the possible $1,800.

JE - Purchase:

Goods   $xxx.xx (net of discount)

        A/P    $xxx.xx (net of discount)

JE - Payment after discount period expires:

A/P $xxx.xx (Net of discount)

Discount lost $xx.xx

             Cash    $xxx.xx (original net $ plus discount lost)

After read both of your explanation, now I understand. Thanks to Nan and mits07.