HPlease help me answer these questions.. i have tried doing it several times but got it incorrect

answer to first twp questions are (1. Gpa is 3.2)

(2. less than a week)

Math 10 MPS Experimental Design Name (gw4) C 1. A researcher wanted to know if students who use the library at a college have higher GPAs than students who do not use the library. The researcher decided to use a random number generator to choose 20 random classes at the college. Students in each of these classes were given surveys that could be filled out anonymously. Students that completed the surveys were given a $5 gift card for the bookstore. 82% of students in the sampled classes returned the surveys. Here are the two questions of interest: How often do you use the library? Never Less than once a week More than once a week, but not every day d. Every day What is your current GPA? a. What method of sampling was used by the researcher? b. Discuss the wording of the questions for possible bias. c. Is this an observational study or an experiment? Explain. d. The researcher concluded that students who use the library more frequently have higher GPAs. Is this a valid conclusion for this type of study? Explain