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A negative number is a number that is less than zero. Negative numbers are often found in everyday life, like in temperatures below freezing, financial debts, or elevations below sea level. In mathematics, negative numbers are represented with a minus sign (-) before the number.
For example, in the exercise, -12.3 is a negative number because it has a minus sign in front. It means the value is 12.3 units less than zero. Remember, negative numbers lie to the left of zero on the number line.

Positive numbers are numbers greater than zero. They are often used to indicate things like profits, temperatures above freezing, or elevations above sea level. In math, positive numbers do not have a sign before them or sometimes have a plus sign (+).
For instance, in the solution to the exercise, the opposite of -12.3 is 12.3, which is a positive number. Positive numbers are located to the right of zero on the number line. They show how far a value is from zero in the positive direction.

The sign of a number indicates if it is positive or negative. Changing the sign of a number involves flipping it from positive to negative or from negative to positive. This process is also called finding the opposite or additive inverse.
In the step-by-step solution, changing the sign of -12.3 means turning it into 12.3. It changes from being 12.3 units less than zero to 12.3 units more than zero. Understanding sign change is crucial in arithmetic and algebra to solve equations and manipulate expressions correctly.

Basic arithmetic includes fundamental operations like addition, subtraction, multiplication, and division. It is the foundation of all other math topics. Understanding how to perform and apply these operations is essential for solving mathematical problems.
In the provided exercise, changing the sign of a number is a simple arithmetic operation. It's essential to understand that flipping the sign does not change the magnitude (absolute value) of the number. So, changing -12.3 to 12.3 maintains the numerical value but changes its direction relative to zero.
These four core concepts interconnect within the exercise, showcasing the importance of understanding negative and positive numbers, how to change their signs, and applying basic arithmetic principles.