Question 14307
You can write the equation to solve this problem like this:

(10%)x liters + (30%)80 liters = (15%)(x+80)liters. Change the percents to decimals.

{{{0.1x + (0.3)80 = (0.15)(x+80)}}} Simplify and solve for x.
{{{0.1x + 24 = 0.15x + 12}}} Subtract 12 from both sides.
{{{0.1x + 12 = 0.15x}}} Subtract 0.1x from both sides.
{{{12 = 0.05x}}} Finally, divide both sides by 0.05
{{{240 = x}}}

240 liters of 10% alcohol solution must be added to the 80 liters of the 30% alcohol solution to obtain 320 liters of 15% alcohol solution.