aplicam regula dreptunghiului................
c1=10% ------------------------> c.f. - c2 = (x-5) parti de masa
c.f.=x%
c2=5% ------------------------> c1-c.f. = (10-x) parti de masa
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total parti de masa = x-5+10-x = 5 parti masa
=> 5 parti masa ..... x-5 parti sol. c1 ................ 10-x parti sol. c2
=> x-5/1 = 10-x/4
=> 4x-20 = 10-x => x = 30/5 = 6%