<PRE><B>Question 214085</B>
Let {{{a}}} = liters of 5% solution
Let {{{b}}} = liters of 20% solution
given:
(1) {{{a + b = 25}}}
Alcohol in 5% solution = {{{.05a}}}
Alcohol in 20% solution = {{{.2b}}}
-------------------------------------
{{{(.05a + .2b)/25 = .14}}}
{{{.05a + .2b = 3.5}}}
(2) {{{5a + 20b = 350}}}
Multiply both sides of (1) by {{{5}}} and subtract from (2)
(2) {{{5a + 20b = 350}}}
(1) {{{-5a - 5b = -125}}}
{{{15b = 225}}}
{{{b = 15}}}
and, since
{{{a + b = 25}}}
{{{a + 15 = 25}}}
{{{a = 10}}}
15 liters of 5% solution and 10 liters of 20% solution are needed
check:
{{{.05a + .2b = 3.5}}}
{{{.05*10 + .2*15 = 3.5}}}
{{{.5 + 3 = 3.5}}}
{{{3.5 = 3.5}}}
OK</PRE>