The number of ways to check off one answer to each question is; 20ways.
The number of ways to check off one answer to each question and get it wrong is; 15ways.
a) Since each question has four possible answers, it therefore follows that the student can choose any of 4 options in each question and consequently, the number of different ways is; 4 × 5 = 20.
b) Since only one option is correct, it follows that there are 3 wrong choices in each question case and hence, the number of ways to pick one wrong answer is; 3 × 5 = 15.
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