c₁=5%
c₂=20%
ms₁/ms₂=1/3
c final = ?
5=md₁*100/ms₁ unde md₁=0,05ms₁
20=md₂*100/ms₂ ⇒₂=0,2ms₂ unde ms₂=3ms₁
c final =md final *100/ ms final
md final - md₁+md₂=0,05ms₁+0,2ms₂=0,05ms₁+0,6ms₁ = 0,65 ms₁
ms final = ms₁+ms₂=4ms₁ ⇒ c final = 0,65ms₁*100/4ms₁ ⇒ c final =16,25%