Question 27931
look at my lesson on this topic on the algebra website.


Let x = number of litres of 15% solution required.


Question is all about "BEFORE mixing" equalling "AFTER mixing"


so BEFORE: xlitres of 15% + 3 litres of 30%
and AFTER: (x+3) litres of 20%


so... 0.15x + 0.30*3 = 0.20(x+3)
0.15x + 0.90 = 0.20x + 0.60
0.90 = 0.05x + 0.60
0.30 = 0.05x
--> x = 0.30/0.05
--> x = 6 litres


Jon.