The problem in a science fair project is the scientific question that the experiment attempts to answer. It should be phrased as a question and begin with a question word such as "how" or "why."
When writing a problem statement for a science fair project, there are a few rules that one should follow. First, the problem should test how the independent variable influences the dependent variable. Next, the question should be interesting and engaging so that the project is not boring to complete. Lastly, the experimenter should find at least three sources of useful information about the subject so that she can conduct adequate research before the experiment.