What does the term "compatible numbers" refer to?

The term "compatible numbers" refers to numbers that can be divided evenly, making calculations simpler and more manageable, particularly in mental math. These numbers typically have factors that are easy to work with, helping to simplify operations like addition, subtraction, multiplication, or division.

For example, when estimating the result of a division problem, compatible numbers can be chosen to make the math straightforward — such as using 60 instead of 58 when dividing by 4, since 60 is a multiple of 4 and results in an exact answer of 15.

In contrast, the other definitions do not capture the essence of compatible numbers as they relate to the ease of calculation and simplification. Thus, recognizing that compatible numbers are those that allow for straightforward division is key to understanding their use in mathematics.