MCa3(PO4)2=masa moleculară a substanței
MCa3(PO4)2=3ACa+2AP+8AO
MCa3(PO4)2=3×40+2×31+8×16=310
1 mol...MCa3(PO4)2...masa de P din MCa3(PO4)2
..................x........................30
1 mol...310g Ca3(PO4)2...62g P
..................x............................30g P
X=30×310/62=150g