Answer
10 gallons of 40% acid solution.
20 gallons of 10% acid solution.
Work Step by Step
Let $x$ be the volume of 40% acid solution needed.
$(30-x)$ is the volume of 10% acid solution needed.
40% = 0.4; 10% = 0.1; 20 = 0.2
$0.4 \times x + 0.1 \times (30-x)=0.2 \times 30$
$0.4x + 3-0.1x=6$
$0.3x+3=6$
$0.3x=3$
$x=10$
10 gallons of 40% acid solution needed.
$30-x=30-10=20$
20 gallons of 10% acid solution needed.
