Question 11328
In the UK, these sort of questions are not common, but there seems to be a lot of these on this site, and they are quite straightforward, really.. so here goes:


Let x = amount of 74% solution.


so, we have 74% amount + 53% amount = 63% amount. The problem is, we are not told how much of the 53% solution was used... call this y for now.


0.74x + 0.53y = 42*0.63


now, x+y=42, so y=42-x, so use this rather than y, giving:
0.74x + 0.53(42-x) = 42*0.63
0.74x + 22.26 - 0.52x = 26.46
0.21x + 22.26 = 26.46
0.21x = 4.20
--> x = 20 litres.


jon.