sole trader

1) A sole trader does not keep proper accounting records, and it is necessary to calculate her total purchases for the year ended 31 january 20×3 from the following information:

trade payables : 31 january 20×2 ……………130,400
31 january 20×3……………..171,250
payment to suppliers …………………………888,400
cost of goods taken from inventory by
sole trader for her personal use ……………..1000
refunds received from suppliers ……………..2400
discounts received …………………………..11,200

what is the figure for purchases that should be included in sole trader’s financial statements?
ans: 937,050
solution: purchase control account

payment to suppliers 888,400 opening balance 130,400
discounts received 11,200 goods taken 1000
closing balance 171,250 refunds 2400
purchase (bal fig) 937050
1070850 1070850

my question is in a purchase account why opening balance in the credit side? I also don’t understand about dis. Received. Can I not solve this problem by payable control acc? Plz help.