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Combinatorics
1.
(13 p.)
Two students Alice and Bob participated in a twoday math contest. At the end both had attempted questions worth 500 points. Alice scored 160 out of 300 attempted on the first day and 140 out of 200 attempted on the second day, so her twoday success ratio was 300/500 = 3/5. Bob’s scores are different from Alice’s (but with the same twoday total). Bob had a positive integer score on each day. However, for each day Bob’s success ratio was less than Alice’s. Assume that \( p/q \) (\( p \) and \( q \) are relatively prime integers) is the largest possible twoday success ratio that Bob could have achieved. Calculate \( p+q \).
2.
(13 p.)
Given a regular 12gon D, determine the number of squares that have two or more vertices among the vertices of D.
3.
(28 p.)
In a tournament club \( C \) plays 6 matches, and for each match the probabilities of a win, draw and loss are equal. If the probability that \( C \) finishes with more wins than losses is \( \frac pq \) with \( p \) and \( q \) coprime \( (q>0) \), find \( p+q \).
4.
(13 p.)
Assume that \( A \) is a 40element subset of \( \{1,2,3,\dots,50\} \), and let \( n \) be the sum of the elements of \( A \). Find the number of possible values of \( n \).
5.
(31 p.)
There are 27 candidates in elections and \( n \) citizens that vote for them. If a candidate gets \( m \) votes, then \( 100m/n \leq m1 \). What is the smallest possible value of \( n \)?
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