Răspuns:
100g solutie.......50gNaOH
20g......................x= 10gNaOH
C=mdx100/ms---> md= cxms/100
c1=80% ------------>md1=0,8ms1 KgH2SO4
c2= 40%;ms2=4kg--> md2= 0,4x4kg=1,6kgH2SO4
C3= 62%=(md1+md2)X100/(ms1+ms2)
62/100=( 0,8ms1+1,60)/(ms1+4)
80ms1+160=62ms1+248----> ms1= 3,9kg