The percentage of phosphorus in the double superphosphate

Ca(H₂PO₄)₂ - double superphosphate

1) Firstly need to know the molar mass
Mr(Ca(H₂PO₄)₂) = 40 + 2·(2+31+64) = 40 + 2·97 = 234 g/mol
2) Find the mass fraction by the formula
ω(R) = , where R - element and RX - substance
ω(P) =  = 25,5 %