Quantitative | Combinatorics question

Can someone explain the following solution for this question? If a student doesn't answer the question, then there should be 2^1 ways, but why is it regarded as 2*2^1 ways?

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In how many ways can the students answer a 10-question true false examination?

(a) In how many ways can the students answer a 10-question true false examination?
(b). In how many ways can the student answer the test in part (a) if it is possible to leave a question unanswered in order to avoid an extra penalty for a wrong
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