Final answer:
The summation of customer account numbers from a batch of sales invoices is an index number used in business to track changes and patterns in sales activity over time.
Step-by-step explanation:
A summation of customer account numbers taken from a batch of sales invoices would be classified as an index number. An index number, in business context, is a statistical measure designed to show changes in a variable or a group of related variables over time. When working with sales invoices, the summation you're describing allows businesses to track changes and patterns in customer purchases or account activity.
Creating index numbers can get complicated when dealing with a larger set of data with prices that include cents or odd amounts, rather than round numbers. This type of analysis is essential for businesses to understand trends and make informed decisions based on the total quantity spent over a year or some other period. Such calculations take into account the diversity of goods and services represented by realistic sales data.