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During a month with 30 days, a cricket team plays at least one game a day, but no more than 45 games. There must be a period of some number of consecutive days during which the team must play exactly ______ number of games.(a) 17(b) 46(c) 124(d) 24I had been asked this question in examination.I'm obligated to ask this question of Counting topic in portion Counting of Discrete Mathematics

Answer»

Correct answer is (d) 24

To elaborate: Let a1 be the number of games played until day 1, and so on, AI be the no games played until i. Consider a sequence like a1,a2,…a30where 1≤ai≤45, ∀ai. Add 14 to each element of the sequence we get a new sequence a1+14, a2+14, … A30+14where, 15 ≤ ai+14 ≤ 59, ∀ai. Now we have two sequences 1. a1, a2, …, a30 and 2. a1+14, a2+14, …, a30+14. having 60 elements in total with each elements taking a value ≤ 59. So according to pigeon hole principle, there must be at LEAST two elements taking the same value ≤59 i.e., ai = aj + 14 for some i and j. THEREFORE, there exists at least a period such as aj to ai, in which 14 matches are played.



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