4

The answer follows from Bertrand's Ballot Theorem:


4

Here is 19


2

For the numbers 2,4,6,8 one solution is (6-2)/4+8=9 For the numbers 4,5,6,8 one solution is 8/(6-4)+5=9


2

We may have ambiguity here, but I will try to answer both cases. Please note there could be more answers, just that I will list one for each case. 8, 6, 4, 2: 8, 6, 4, 5:


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