Question 622586
Note that {{{ 1.2x + 1.4y }}} is the total cost of
the o.j. and p.j. used.
So you need to divide this by total liters needed
to get the cost/liter
(1) {{{ ( 1.2x + 1.4y ) / 8 = 1.24 }}}
and the other equation is:
(2) {{{ x + y = 8 }}}
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(1) {{{ 1.2x + 1.4y = 1.24*8 }}}
(1) {{{ 1.2x + 1.4y = 9.92 }}}
(1) {{{ 120x + 140y = 992 }}}
Multiply both sides of (2) by {{{ 120 }}}
and subtract (2) from (1)
(1) {{{ 120x + 140y = 992 }}}
(2) {{{ -120x - 120y = -960 }}}
{{{ 20y = 32 }}}
{{{ y = 1.6 }}}
and, since
(2) {{{ x + y = 8 }}}
(2) {{{ x + 1.6 = 8 }}}
(2) {{{ x = 6.4 }}}
6.4 liters of OJ and 1.6 liters of PJ are needed
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check answer:
(1) {{{ ( 1.2x + 1.4y ) / 8 = 1.24 }}}
(1) {{{ ( 1.2*6.4 + 1.4*1.6 ) / 8 = 1.24 }}}
(1) {{{ ( 7.68 + 2.24 ) / 8 = 1.24 }}}
(1) {{{ 9.92 / 8 = 1.24 }}}
(1) {{{ 9.92 = 9.92 }}} 
OK