Answer:
Amount of sleep
Step-by-step explanation:
There are two types of variables in a scientific experiment.
Independent variable: An independent variable can be described as the variable which is changed or can be controlled during the experiment. The effects of the independent variables on the dependent variable are tested.
In the scenario discussed in the question, amount of sleep will be independent variable as it is not dependent on any other factor.
Dependent variable: It is the variable which is being tested or measured due to changes in the independent variable.
In the scenario discussed in the question, the exam score will be the dependent variable as it will be dependent on the independent variable i.e amount of sleep.