Calculating equilibrium constants?

equilibrium constant formula is K= [products]/[reactants] were [] means concentration or M. So from the problem it states how there is 1 mol of PCl5 in a 10.0 l flask. You can find the molar concentration of the reactant which is 1/10= 0.1 M PCl5. Now the products are Cl2 and PCl3 it gave you the moles of chlorine so divide it by 10.0 L to find the molar concentratino of chlorine and the PCl3 will be the same as chlorine. So the concentratino of PCl5 is 0.1 M, PCl3 and Cl2 are both 0.047 M. Now the Kc would just be [PCl5]/([Cl2]*[PCl3]. so the Kc is 0.1/(0.047)^2......and i am not sure how to do the fraction dissociated you may need more info..i hope this has helped you out