Answer:
In a complex model, scientists use variables to simplify calculations.
Step-by-step explanation:
Variables are values or quantities that can change within a model. They allow scientists to represent complex relationships and systems with a smaller number of inputs. By using variables, scientists can perform mathematical operations and make predictions about the behavior of the system being modeled. For example, in a model of a population, a variable might represent the number of individuals in the population, while another variable might represent the birth rate. By manipulating these variables, scientists can make predictions about how the population will change over time.