You basically see if statements are correct or not. Remember this is sample, sample is portion of population so if everything is dome correctly, the results of sample will also display the results of population +- error (standard deviation). So you can just use the sample results to answer questions about the population.
A is correct because social studies has 4 students and reading has 8. Math has twice. B is correct because reading has 2 and math has 8. Reading is one fourth of math 8*1/4 = 8/4=2. D is NOT correct because math is 8, social studies is 4. Math is not half of social studies. Social studies is half of math.
