How can i calculate the concentration of each ions remaining in the solution after precipitation is complete?

ok heres the full question::
2KOH + Mg(NO3)2 -------------> 2KNO3 + Mg(OH)2
a 100.0 mL aliquot of 0.200 M aqueous potassium hydroxide is mixed with 100.0mL of 0.200M (aq) Magnesium nitrate. it had previously asked for the mass of precipitation produced..and that was 0.583 g Mg(OH)2 . i really don't know how to calculate the concentration of the remaining ions

K+
Mg2+
OH-
NO3-
i know OH- is equal to 0 because its the limiting reagent but for the life of me i cant figure out how to do the rest. could some one please explain it to me.