Final answer:
An integer that is not a whole number is -1 because whole numbers are non-negative integers starting from 0, while integers include negative numbers as well. All whole numbers are integers, but the converse is not true.
Step-by-step explanation:
A number that is an integer but not a whole number is -1. This number is an integer because it does not have a fractional or decimal component and belongs on the number line among integers. However, it is not considered a whole number, because whole numbers are all non-negative integers, starting from 0 and increasing to infinity. In contrast, integers include all whole numbers and their negative counterparts. It's essential to understand that while all whole numbers are integers, not all integers are whole numbers.
The system of numbers that we use, based on the digits 0 through 9, allows us to write numbers with or without a decimal point. If there's no decimal point marked, it is assumed to be at the rightmost end of the number. For instance, 123 can also be written as 123.0 with the decimal point included. This illustrates that integers can be expressed in a decimal form but still remain integers as long as they don't have any non-zero digits beyond the decimal point.
Integers are useful in a wide array of applications, from counting and measuring to more advanced mathematical operations like powers (e.g., 4³, which is a shorthand for 4 x 4 x 4). It's important to remember that integers are a foundational part of mathematics that help us understand and perform various calculations.