Set P={x|2≤x≤5}

Q={x|k+ 1≤x≤2k- 1}

If P∩Q= empty set,

Discuss in two situations:

When q is an empty set, k+1>; 2k- 1, k<2. Satisfy the meaning of the problem.

When q is not an empty set, k+ 1≤2k- 1, k≥2.

There are k+ 1 > 5 or 2k- 1 < 2.

Then k > 4 or k < 3/2.

And because k≥2.

So k > 4.

To sum up, is k > 4 or K?