Question 1079833
Let {{{ d }}} = the distance to his girlfriend's house
Let {{{ s }}} = his running speed in mi/hr
(1) {{{ d = s*1 }}}
(2) {{{ d = ( s-20 )*2 }}}
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Plug (1) into (2)
(2) {{{ s = ( s-20 )*2 }}}
(2) {{{ s = 2s - 40 }}}
(2) {{{ s = 40 }}}
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Plug this result into (1)
(1) {{{ d = 40*1 }}}
(1) {{{ d = 40 }}}
His girlfriend lives 40 mi away
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check:
(2) {{{ d = ( s-20 )*2 }}}
(2) {{{ d = ( 40-20 )*2 }}}
(2) {{{ d = 20*2 }}}
(2) {{{ d = 40 }}} mi
OK