Question 557673
Let {{{ d }}} = distance in miles they went into country
Let {{{ t }}} = time in hrs to go into country
{{{ 7 - t }}} = time in hrs to get back
Going into country:
(1) {{{ d = 40t }}}
Coming back:
(2) {{{ d = 30*( 7 - t ) }}}
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By substitution:
{{{ 40t = 30*( 7 - t ) }}}
{{{ 40t = 210 - 30t }}}
{{{ 70t = 210 }}}
{{{ t = 3 }}}
and
(1) {{{ d = 40t }}}
(1) {{{ d = 40*3 }}}
(1) {{{ d = 120 }}}
They went 120 miles into country
check:
(2) {{{ d = 30*( 7 - t ) }}}
(2) {{{ d = 30*( 7 - 3 ) }}}
(2) {{{ d = 120 }}}
OK