when preparing a representative sample from a list of 200 customers who complained about errors in their statements, a could ensure the sample is balanced geographically by selecting five customers from each of four zip codes.

Stratified sample

Explanation:

For preparing samples of various data of companies and enterprises we need to apply probability distribution to different samples of data. Here in the question we are to apply a representative sample from a list of 200 customers who have complained about errors in their statement. So here we can apply stratified sampling where we can divide the 200 customers into separate groups. These sub groups of the customers are known as stratas. These stratas are selected based on certain characteristics which can be identified among the customers group. Here we can form subgroups based on the type of complain that has been lodged by the customer and selecting 5 customers from four zip codes. Then it would be easy to apply probability distribution to the sub groups to derive information from them.

This process would also enable a more easier and cheaper way of sampling the customer data.