se calculeaza masa moleculara
MMgCO3=24+12+3.16=84------>1mol=84g
comp. proc. prin masa moleculara
84g MgCO3--------24Mg----------12g C---------48g O
100g-------------------x--------------------y-----------------z
x=100.24: 84=28,57 la suta Mg
y=100.12: 84=14,28 la suta
z=100.48 :84=57,14 la suta