Final answer:
The priority sequencing rule used to order customers standing in a line is first-come, first-served.
Step-by-step explanation:
The priority sequencing rule that is usually used to order customers standing in a line is first-come, first-served. This means that the customer who arrives first is served first, and the rest of the customers are served in the order of their arrival.
For example, if three customers are standing in line and customer A arrives before customer B and customer C, then customer A will be served first, followed by customer B, and then customer C.
This rule is commonly used in various businesses such as restaurants, grocery stores, banks, and retail stores to ensure fairness and efficiency in serving customers.