Question 360921
Let A be the amount of 20% acid solution, and B the amount of 50% acid solution.
1.{{{A+B=600}}}
.
.
{{{20A+50B=30(600)}}}
2.{{{2A+5B=1800}}}
Multiply eq. 1 by -2 and add to eq. 2,
{{{-2A-2B+2A+5B=-1200+1800}}}
{{{3B=600}}}
{{{highlight(B=200)}}}liters
Then from eq. 1,
{{{A+200=600}}}
{{{highlight(A=400)}}}liters