Question 851321
Let {{{ d }}} = distance driven on the freeway in miles
Let {{{ s }}} = Harry's speed on freeway in mi/hr
{{{ 637 - d }}} = distance driven on country road
{{{ s - 20 }}} = Harry's speed on country road
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Equation for freeway:
(1) {{{ d = s*6 }}}
Equation for country road:
(2) {{{ 637 - d = ( s - 20 )*5 }}}
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Substitute (1) into (2)
(2) {{{ 637 - 6s = ( s - 20 )*5 }}}
(2) {{{ 637 - 6s = 5s - 100 }}}
(2) {{{ 11s = 737 }}}
(2) {{{ s = 67 }}}
Harry's speed on freeway was 67 mi/hr
check:
(1) {{{ d = s*6 }}}
(1) {{{ d = 67*6 }}}
(1) {{{ d = 402 }}}
and
(2) {{{ 637 - d = ( 67 - 20 )*5 }}}
(2) {{{ 637 - d = 47*5 }}}
(2) {{{ d = 637 - 235 }}}
(2) {{{ d = 402 }}}
OK