an educational psychologist studies the effect of frequent testing on retention of class material. in one section of an introductory course, students are given quizzes each week. a second section of the same course receives only two tests during the semester. at the end of the semester, both sections take the same final examination. the summarized scores are as follows: (a) frequent quizzes--n=20, m=73, sample variance= 84 and (b) two tests--n=20, m=68, sample variance=96. use a two-tailed test with preset alpha=.05. provide the t statistic, df, critical value, and decision regarding the null hypothesis.