posted by steve .
charlie has 80 ml of a 15% acid solution how much of a 20% acid slolution must be added to create a solution that is 18% acid.
Let x be the number of ml that must be added. The amount of acid contained in the mix can be written two ways, and is:
0.15*80 + 0.20x = 0.18*(80 + x)
Solve for x
12 + 0.20x = 14.4 + 0.18x
0.02x = 2.4
x = 120 ml