The bookkeeper of Floore Company records credit sales in a sales journal and returns in a general journal. The bookkeeper did the following:

1. Recorded an$18 credit sale as $180 in the sales journal
2. Correctly recorded a $40 sale in the sales journal but posted it to B. Blue's account as $400 in the accounts receivable ledger
3. Made an addition error in determining the balance of J. B. Window Co. in the accounts receivable ledger.
4. Posted a sales return that was recorded in the general journal to the sales returns and allowances account and the account receivable account but forgot to record it to the B. Katz Co.
5. Added the total of the sales column incorrectly.
6. Posted a sales return to the account receivable account but not to the sales returns and allowances account. Accounts receivable ledger was recorded correctly.

I dont understand when each error would be discovered.