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Shashank Shekhar Grade: 12

7 years ago

Answers : (1)

Vijay Luxmi Askiitiansexpert
357 Points

Dear Shashank,

The no of students answering exactly p(1≤p≤n-1) questions wrongly is 2n-p - 2n-p-1

The no of students answering all n questions wrongly is 20. Thus, the total no of wrong answers is:

= 1(2n-1 – 2n-2) + 2(2n-2 – 2n-3) + ……..+(n-1)(21 – 20) + n(20)

=> 2n-1 + 2n-2 + 2n-3 + …..+20=2n – 1

=> 2n – 1=2047

=> 2n = 2048

=> n=11


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Vijay Luxmi

7 years ago
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