Pai, afli md pentru solutiile de NaOH -> c =md*100/ms deci md =c*ms/100, atunci md1 =10*400/100 =40g NaOH si md2 =50*400/100 =200g NaOH. md final va fi md1+md2 adica 40+400 = 440 si ms final va fi masa tuturor solutiilor amestecate, adica 400+400+200 =1000g => c final = 440*100/1000 = 44%