Calculate percentage composition of the elements in calcium phosphate Ca₃(PO₄)₂.

Relative molecular mass of Calcium phosphate, Ca₃(PO₄)₂
     = 3 x 40 + 2(31 + 4 x 16)
     = 120 + 2(31 + 64)
     = 120 + 190
     = 310 amu

310 g of Ca₃(PO₄)₂ contains 120 g of Calcium

∴ 100 g of Ca₃(PO₄)₂ contains $\dfrac{120 \times 100}{310}$ g of Calcium

= $\dfrac{12000}{310}$ = 38.70 % of Calcium.

310 g of Ca₃(PO₄)₂ contains 62 g of Phosphorus

∴ 100 g of Ca₃(PO₄)₂ contains $\dfrac{62 \times 100}{310}$ g of Phosphorus

= $\dfrac{6200}{310}$ = 20 % of Phosphorus.

310 g of Ca₃(PO₄)₂ contains 128 g of Oxygen.

∴ 100 g of Ca₃(PO₄)₂ contains $\dfrac{128 \times 100}{310}$ g of Oxygen.

= $\dfrac{12800}{310}$ = 41.3 % of Oxygen.

∴ In Ca₃(PO₄)₂ : Ca = 38.70%, P = 20% and O = 41.3%