Question 373879
In words:
(juice)/(total solution) = 15%
Let {{{a}}} = liters of 30% of needed
Let {{{b}}} = liters of 5% of needed
given:
(1) {{{ a + b = 25}}}
{{{.3a + .05b}}} = juice in 30% and 5% oj
---------------
{{{(.3a + .05b)/25 = .15}}}
{{{.3a + .05b = 3.75}}}
(2) {{{30a + 5b = 375}}}
Multiply both sides of (1) by {{{5}}}
and subtract from (2)
(2) {{{30a + 5b = 375}}}
(1) {{{ -5a - 5b = -125}}}
{{{25a = 250}}}
{{{a = 10}}}
and, since
{{{a + b = 25}}}
{{{b = 25 - 10}}}
{{{b = 15}}}
10 liters of 30% oj and 15 liters
of 5% oj are needed