Question

How many variables should be manipulated in a correctly performed scientific experiment

Answer 1

One, if more than one variable changes in an experiment it will not be possible to tell which is responsible for any changes in the dependent variable, so the experiment will not be very informative.

Answer 2

Answer;

-One variable.

Explanation;

One variable should be manipulated in a correctly performed controlled scientific investigation.

-A variable is any factor, trait, or condition that can exist in differing amounts or types. Variables may be independent, dependent, and controlled. Independent variable is the variable that is changed or controlled in a scientific experiment. Dependent variable is the type of variable that is observed or measured in the experiment.