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In an examination 20question of true-fal...

In an examination 20question of true-false are asked. Suppose a student tosses a fair coin to determine his answer to each question. If the coin falls heads, the answer 'true', if it falls tails, he answers. 'false' find the probabilities that he answers at least 12 questions correctly

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The correct Answer is:
`((1)/(2))^(20)[20C_(12)+""^(20)C_(13)+...+""^(20)C_(20)]`
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