There is this question on my test:

a social networking site recorded that 80% of the people who became members of the site one month were between 30 and 40 years old. the equation below represents this information, where x represents the total number of people who became members of the site that month.

x = 0.8x + 72

how many people who became members of the site that month were between 30 and 40 years of age?

112

288

360

432

i keep getting 360! i submitted it and it was incorrect, what am i doing wrong? ?

The first-serve percentage of a tennis player in a match is normally distributed with a standard deviation of 4.3%. if a sample of 15 random matches of the player is taken, the mean first-serve percentage is found to be 26.4%. what is the margin of error of the sample mean? a. 0.086% b. 0.533% c. 1.11% d. 2.22%

Which graph depicts the path of a projectile

Stu and ambrose are working together on a study of whether diet is related to students' mental health. first, they randomly select 10 students from the student center and 10 students from the office of counseling and psychological services. then, they ask students to rate their diet in terms of healthiness on a scale of 1-100 before completing a 20-item mental health survey. a) name one of the constructs being studied b) how was the construct you named above operationally defined in this experiment? e) was the variable you described above their independent variable, their dependent variable, or a controlled variable? d) what is a confounding variable? what is a potential confound in this study?