Paper 1 October/November 2011 Accounting (9706/11) A Level

Douglas prepared a trial balance and found that the total of the debit column was $50 higher than
the total of the credit column. The following errors were discovered.
error 1 a purchases invoice for $100 had been incorrectly recorded
error 2 an irrecoverable debt of $50 had been incorrectly recorded
Which combination of the two errors together caused the difference in the totals?