Question 953475
Let {{{ s }}} = his average speed before lunch
Let {{{ d }}} = the distance in miles he drove before lunch
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Before lunch:
(1) {{{ d = s*4 }}}
After lunch:
(2) {{{ 400 - d = ( s - 10 )*5 }}}
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Substitute (1) into (2)
(2) {{{ 400 - 4s = 5s - 50 }}}
(2) {{{ 9s = 450 }}}
(2) {{{ s = 50 }}}
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His average speed before lunch was 50 mi/hr
check:
(1) {{{ d = s*4 }}}
(1) {{{ d = 50*4 }}}
(1) {{{ d = 200 }}}
and
(2) {{{ 400 - d = ( s - 10 )*5 }}}
(2) {{{ 400 - 200 = ( 50 - 10 )*5 }}}
(2) {{{ 200 = 40*5 }}}
(2) {{{ 200 = 200 }}}
OK