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A problem with setsby dapet
Tags: sets 
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#1
May204, 10:55 AM

P: 11

Let's imagine two sets A = {1,2,...,k} and B = {1,2,...,k} for some natural k, then let's create n twoelement sets X_1,X_2,...,X_n such that for each 0<i=<n X_i = {a,b} where a is from A and b is from B but a<>b. We know how do sets X_i look like and according to this we will choose the set C = {c_1,c_2,...,c_k} where c_i=i such that the number (denoted MAX) of sets X_1,X_2,...,X_n that have at least one common element with C is maximal. Determine the maximal constant 0<=c<=1 such that MAX>=[cn] for arbitrary n,k and sets X_1,X_2,...,X_n.
NOTE: [x] denotes the integral part of number x Example: k = 2, A = {1,2}, B = {1,2} n = 4, X_1 = {1,2}, X_2 = {1,2}, X_3 = {1,2}, X_4 = {1,2} we can choose C = {1,2} (in this case we have more possibilities) the number X_i that have at least one common element with C is 3, X_1 and C have no common element. From this example we can easily see, that c<=3/4, I think that c=3/4 is sufficient condition, but I can't prove it. Could anybody help me with it? Thanks. 


#2
May1704, 03:02 PM

Sci Advisor
HW Helper
P: 2,586

This doesn't make a whole lot of sense. For one:



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