Question 545080
Let {{{a}}} = pounds of soybean meal needed
Let {{{b}}} = pounds of cornmeal needed
given:
(1) {{{ a + b = 360 }}}
(2) {{{ ( .18a + .09b ) / 360 =  .17 }}}
--------------------------
(2) {{{ .18a + .09b = .17*360 }}}
(2) {{{ .18a + .09b = 61.2 }}}
(2) {{{ 18a + 9b = 6120 }}}
---------------------
Multiply both sides of (1) by {{{9}}},
and subtract (1) from (2)
(2) {{{ 18a + 9b = 6120 }}}
(1) {{{ -9a - 9b = -3240 }}}
{{{ 9a = 2880 }}}
{{{ a = 320 }}}
and, since
(1) {{{ a + b = 360 }}}
(1) {{{ 320 + b = 360 }}}
(1) {{{ b = 40 }}}
320 pounds of soybean meal are needed
40 pounds of cornmeal are needed
check answer:
(2) {{{ ( .18a + .09b ) / 360 =  .17 }}}
(2) {{{ ( .18*320 + .09*40 ) / 360 =  .17 }}}
(2) {{{  57.6 + 3.6 = .17*360 }}}
(2) {{{ 61.2 = 61.2 }}}
OK