se aplica regula dreptunghiului:
25%-------------------> 20-5 = 15 parti sol. 25%
l l
l 20% l
l l
5%--------------------> 25-20 = 5 parti sol. 5%
-------------------------------
total = 5+15 = 20 parti sol 20%
20 parti sol ..... 5 parti sol. 5% ..... 15 parti sol. 25%
400 g ................X g sol. 5% ........... Y g sol 25%
X = 400x5/20 = 100 g sol. 5%
Y = 400x15/20 = 300 g sol. 25%