Taking into account that Normality of NaOH =N1=0.2115 N Volume of NaOH =V1=27.31 ml Normality of HCl =N2=x N Volume of HC l=37.45 ml We may proceed like this: V1*N1=V2*N2 27.31*0.2115=37.45*x , x=0.1542 N=0.1542 M . Concentration of HCl = 0.1542 moles/liter. Hope this is good for you