Guten Abend Anonymous,
819,04 => 100 %
21,52 => p % => $${\mathtt{p}} = {\frac{{\mathtt{21.52}}{\mathtt{\,\times\,}}{\mathtt{100}}}{{\mathtt{819.04}}}} \Rightarrow {\mathtt{p}} = {\mathtt{2.627\: \!466\: \!302\: \!012\: \!111\: \!7}}$$ [ % ]
21,52 = 2,627 % von 819,04
Probe: $${\mathtt{819.04}}{\mathtt{\,\times\,}}{\mathtt{2.627}}\% = {\mathtt{21.516\: \!180\: \!8}}$$
Oder so rechnen:
x * 819,04 = 21,52 $${\mathtt{x}} = {\frac{{\mathtt{21.52}}}{{\mathtt{819.04}}}} \Rightarrow {\mathtt{x}} = {\mathtt{0.026\: \!274\: \!663\: \!020\: \!121\: \!1}}$$
$${\mathtt{x}} = {\frac{{\mathtt{0.026\: \!27}}}{{\mathtt{1}}}} = {\frac{{\mathtt{2.627}}}{{\mathtt{100}}}} = {\mathtt{2.627}}\%$$
Gruß radix 
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+14538 
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