1.
200g-100%
x-15%
x=200*15%/100%=30[g]=waga soli kuchennej
200g-30g=170g=waga wody
2.
300g-100%
6g -x
x=6g*100%/300g=2%
3.
500g-100%
x-1%
x=500g*1%/100%=5g=waga chlorku magnezu
500g-5g=495g=waga wody
d=gęstośc
d wody=1g/cm3
m=495g
V=?
d=m/V
V=m/d
V=495g/(1g/cm3)
V=495cm3