13. C=md/ms*100=> md=C*ms/100=12*400/100=48g
ms=md+mH2O=>mH2O=ms-md=400-48=352g
Formulă de calcul prescurtat => C*mH2O=md(100-C) <=> 24*mH2O=48(100-24) => mH2O=48(100-24)/24 = 152g
mH2O evaporată = 352-152=200g
14. C=md/ms*100=>md=C*ms/100=20*500/100=100g
msf = 500-100=400g
Cf=md/msf*100=100/400*100=25℅
18. C*mH2O=md(100-C) => mH2O=md(100-C)/C = 39(100-13)/13 = 261g