Question 699323
(1) {{{ x + y = 500 }}}
(2) {{{ 44x + 28y = 17200 }}}
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(2) {{{ 11x + 7y = 4300 }}}
Multiply both sides of (1) by {{{  7 }}}
and subtract (1) from (2)
(2) {{{ 11x + 7y = 4300 }}}
(1) {{{ -7x - 7y = -3500 }}}
{{{ 4x = 800 }}}
{{{ x = 200 }}}
and, since
(1) {{{ x + y = 500 }}}
(1) {{{ 200 + y = 500 }}}
(1) {{{ y = 300 }}}
He should plant 200 acres of corn 
and 300 acres of wheat
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check:
(2) {{{ 44*200 + 28*300 = 17200 }}}
(2) {{{ 8800 + 8400 = 17200 }}}
(2) {{{ 17200 = 17200 }}}
OK