Question 28406
mixture questions are all about BEFORE and AFTER...they have to be equal.


Let x=amount of 10% acid to be added.
and so how much of the 20% acid? Leap of faith... it is everything else of the 10litres of the final amount surely? so (10-x)litres of the 20% acid.


--> 0.10*x + 0.20(10-x) is everything before mixing.


After mixing, we have 10 litres of a 12% acid --> 0.12*10


so 0.10*x + 0.20(10-x) = 0.12*10
0.1x + 2 - 0.2x = 1.2
-0.1x + 2 = 1.2
-0.1x = -0.8
x = -0.8/-0.1
x = 8 litres


and so we need 8 litres of the 10% acid and 2 litres of the 20% acid.


Easy? :-)


jon.