Question 665218
The way I do it is to solve it in a straightforward way,
and then I can build any kind of table I want
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Let {{{ a }}} = pounds of soybean meal needed
Let {{{ b }}} = pounds of corn meal needed
{{{ .16a }}} = pounds of protein in {{{ a }}} pounds of soybean meal
{{{ .09b }}} = pounds of protein in {{{ b }}} pounds of cornmeal
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(1) {{{ a + b = 350 }}}
(2) {{{ ( .16a + .09b ) / 350 = .12 }}}
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(2) {{{ .16a + .09b = .12*350 }}}
(2) {{{ .16a + .09b = 42 }}}
(2) {{{ 16a + 9b = 4200 }}}
Multiply both sides of (1) by {{{9}}} and
subtract (1) from (2)
(2) {{{ 16a + 9b = 4200 }}}
(1) {{{ -9a - 9b = -3150 }}}
{{{ 7a = 1050 }}}
{{{ a = 150  }}}
and, since
(1) {{{ a + b = 350 }}}
(1) {{{ 150 + b = 350 }}}
(1) {{{ b = 200 }}}
150 pounds of soybean meal are needed
200 pounds of corn meal are needed
check answer:
(2) {{{ ( .16*150 + .09*200 ) / 350 = .12 }}}
(2) {{{ ( 24 + 18 ) / 350 = .12 }}}
(2) {{{ 42 / 350 = .12 }}}
(2) {{{ 42 = .12*350 }}}
(2) {{{ 42 = 42 }}}
OK- now you can make a table