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PTK: CO2= 12+16.2=44 amu

%C=12.1.100%/44=27%

%O=100%-27%=73%

PTK: KNO3=39+14+16.3=101 amu

%K= 39.1.100%/101=39%

%N=14.1.100%/101=14%

%O=100%-39%-14%=47%

PTK: CuSO4= 64+32+16.4=160 amu

%Cu= 64.1.100%/160=40%

%S=32.1.100%/160=20%

%O=100%-40%-20%= 40%