Final answer:
The auditor concerned with the number of sales invoices containing mathematical errors would use attribute sampling to estimate the rate of occurrence of this characteristic.
Step-by-step explanation:
If an auditor, planning to use statistical sampling, is concerned with the number of a client's sales invoices that contain mathematical errors, the auditor would most likely utilize attribute sampling. Attribute sampling is used when the audit objective is to estimate the rate of occurrence of a specific characteristic, such as mathematical errors in sales invoices. Attribute sampling allows the auditor to reach a conclusion about the population in terms of a rate or percentage.
The other types of sampling mentioned, namely variable sampling, discovery sampling, and probability proportional to size (PPS) sampling, serve different purposes. Variable sampling is used to estimate the monetary value of a population, discovery sampling is used when the occurrence of a characteristic is particularly critical or an error rate is expected to be low, and PPS sampling is used to test for overstatement errors where the sampling units are selected in proportion to their monetary value.