Question 773257
Let {{{ d }}} = the one-way distance to friends house
Let {{{ t }}} = time spent driving at {{{ 40 }}} mi/hr
{{{ 4 - t }}} = time spent driving at {{{ 45 }}} mi/hr
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Equation for driving to house
(1) {{{ d = 40t }}}
Equation for driving back:
(2) {{{ d = 45*( 4 - t ) }}}
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Substitute (1) into (2)
(2) {{{ 40t = 45*( 4 - t ) }}}
(2) {{{ 40t = 180 - 45t }}}
(2) {{{ 85t = 180 }}}
(2) {{{ t = 2.1176 }}}
and, since
(1) {{{ d = 40*2.1176 }}}
(1) {{{ d = 84.706 }}}
{{{ 2d = 169.412 }}}
He traveled 169.412 miles