1. A dentist is interested in knowing if it is a true claim by crest that brushing your teeth twice a day with their whitening toothpaste will make your teeth whiter than only brushing with it once a day. The dentist tests 20 people who brush once a day with the whitening toothpaste, and 20 who do twice a day like Crest recommends to see how big the change in brightness is over the course of a month. The toothpaste used is the exact same for both groups.

1.Identify the dependent variable.

2. Identify the independent variable and its levels.

3. What is the null hypothesis?

4. What is the alternative hypothesis?