Examination again

For a set of 10 true or false questions , no two students have given the same sequence of answers. What is the maximum number of students who passed in exam if the ratio of students passed to students who failed is 8 : 3 8:3 ?


The answer is 744.

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1 solution

Since no two students have given the same sequence of answers, the number of students is less than or equal to the number of possible sequences = 2 1 0 = 1024 2^10 = 1024

If n 1024 n \le 1024 is the total number of students, then the number of passed students = 8 11 n \frac{8}{11}n .

For the number of passed students to be an integer (and be maximum), n n should chosen as the number divisible by 11 and less than 1024. This gives n = 1023 n = 1023

and passed students = 8 11 1023 = 744 \frac{8}{11}1023 = \boxed{744}

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