Question 379008
Pure acid is a 100% solution.
Let A be the amount of pure acid.
Let B be the amount of 10% solution. 
1.{{{A+B=54}}}
.
.
2.{{{100A+10B=20(54)}}}
{{{10A+B=108}}}
Subtract eq. 1 from eq. 2,
{{{10A+B-A-B=108-54}}}
{{{9A=54}}}
{{{highlight(A=6)}}}liters
Then from eq. 1,
{{{highlight(B=48)}}}liters