In a different population, suppose that 38.40% of people are blood type A, and 46.24% are blood type O. Assuming this population is in Hardy-Weinberg equilibrium, what percentage of the population is blood type B

We can break this down:
The student has a one out of five chance of getting a correct answer, and a four out of five chance of an incorrect answer. We can express the students odds of getting one incorrect answer as 4/5. In order to get the odds of two wrong answers, we need to multiply this answer again by the odds of choosing a wrong answer. Therefore:
The odds of one wrong answer = 4/5
The odds of two wrong answers = (4/5) * (4/5) = 16/25 chance of getting both of the questions wrong.