Question 342508
Hint: Think about 'x' being in slot 1, 'y' being in slot 2, etc all the way up to 'v' being in slot 5. So if order mattered, then {x,y,z,u,v} would mean that x maps to 1, y maps to 2, etc. On the other hand, if we have {y, z, u, v, x}, then y now maps to 1, z maps to 2, etc. 


If you can think of it like that, then it really comes down to a problem about combinatorics (ie permutations and combinations).