Final answer:
In the 1900 date system used by programs like Microsoft Excel, the date 1/1/1900 corresponds to the number 1. This is part of a date serial number system that helps with calculations and data manipulation within software.
Step-by-step explanation:
When using the 1900 date system, the date 1/1/1900 is the equivalent to the number 1. This system is commonly used in spreadsheet programs such as Microsoft Excel, where the date 1/1/1900 is assigned the serial number 1. This serial number format allows for dates to be manipulated and formatted within the software. It's important to note that handling dates in computing can be complex due to various calendar systems and the need for accurate calculations, as seen during the Year 2K transition.