[brentr]

A Cu/Cu^2+ concentration cell has a voltage of 0.23V at 25C.  The concentration of Cu^2+ in one of the half cells is 1.6x10^-3M.  What is the concentration of Cu^2+ in the other half-cell?

This is what I have worked out, but the answer does not seem to be correct...
 Oxidation half cell :
           Cu  ---- >  Cu+2  + 2e
         Reduction half cell :
             Cu+2   + 2e  ------>  Cu
        Net cell Reaction:
               Cu  +  Cu+2  ------>  Cu+2  + Cu
           Ecell  =  E0cell  - 0.059 / 2  log [ Cu+2 ]  /  [ Cu+2 ]
          0.23 V   =  + 0.340 V  - 0.059 / 2  log [ 1.6 x 10-3 M ]  /  [ Cu+2 ]
              [ Cu+2 ]   = 3.048 x 10-7 M

[Borek]

In concentration cell E0 doesn't matter, it should cancel out.