Let the number of liters of 20% solution be "x"
Let the number of liters of 70% solution be "y"
According to the problem, we need 50 liters of the solution. Thus, we can write >>>>
[tex]x+y=50[/tex]Also, given, we need 50 L of 60% solution. Thus, we can write >>>>>
[tex]0.2x+0.7y=0.6\times50[/tex]Let's substitute first equation into the second and solve for "x" >>>>>
[tex]\begin{gathered} x+y=50 \\ 0.2x+0.7y=0.6\times50 \\ --------------- \\ y=50-x \\ \text{Substituting,} \\ 0.2x+0.7(50-x)=30 \\ 0.2x+35-0.7x=30 \\ 0.5x=5 \\ x=\frac{5}{0.5} \\ x=10 \end{gathered}[/tex]So, the "y" value is >>>
[tex]\begin{gathered} x+y=50 \\ 10+y=50 \\ y=50-10 \\ y=40 \end{gathered}[/tex]So, he needs,
Answer10 liters of 20% solution
40 liters of 70% solution