Question 963835
Let {{{ p }}} = number of pigs
Let {{{ c }}} = number of chickens
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(1) {{{ p + c = 50 }}}
(2) {{{ 4p + 2c = 140 }}}
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(2) {{{ 2p + c = 70 }}}
Subtract (1) from (2)
(2) {{{ 2p + c = 70 }}}
(1) {{{ -p - c = -50 }}}
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{{{ p = 20 }}}
He has 20 pigs
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check:
(1) {{{ 20 + c = 50 }}}
(1) {{{ c = 30 }}}
and
(2) {{{ 2p + c = 70 }}}
(2) {{{ 2*20 + 30 = 70 }}}
(2) {{{ 40 + 30 = 70 }}}
(2) {{{ 70 = 70 }}}
OK