Audit procedure 1 During controls testing the auditors selected a sample of purchase invoices and examined them for evidence of an appropriate person authorising the invoice prior to payment. The sample was chosen by selecting every 30th invoice in the population. Audit procedure 2 During substantive procedures the auditors selected a sample of balances included in the trade receivables figure and wrote to the supplier asking them to confirm the amount owed to the audit client at the year-end. The sample was chosen by the auditor without following a structured technique, in an attempt to ensure that all balances had a chance of selection. Identify the ISA 500 (Audit evidence) evidence gathering technique and the sampling method used by the auditors in each of these procedures