continut sau puritate sunt similare.
10,5 t carbune (masa impura) ................ 100%
m.pura ........................................................ p=75%
= 7,875 t carbon
sau
p% = m.purax100/m.impura
=> m.pura = m.impuraxp%/100
= 10,5x75/100 = 7,875 t carbon
m.impuritati = m.impura - m.pura
= 10,5 - 7,875 = 2,625 t impuritati