Question 820558
Let {{{ r }}} = his rate on foot
{{{ 4r }}} = his rate on a bicycle
Let {{{ t }}} = his time in hours on foot
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Equation for walking:
(1) {{{ 12 = r*t }}}
Equation for biking:
(2) {{{ 12 = 4r*( 5 - t ) }}}
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(1) {{{ t = 12/r }}}
and
(2) {{{ 12 = 20r - 4r*t  }}}
Substitute (1) into (2)
(2) {{{ 12 = 20r - 4r*(12/r)  }}}
(2) {{{ 12 = 20r - 48 }}}
(2) {{{ 20r = 60 }}}
(2) {{{ r = 3 }}}
His rate of walking was 3 mi/hr
check:
(1) {{{ 12 = 3*t }}}
(1) {{{ t = 4 }}}
and
(2) {{{ 12 = 4*3*( 5 - t ) }}}
(2) {{{ 12 = 12*( 5 - t ) }}}
(2) {{{ 12 = 60 - 12t }}}
(2) {{{ 12t = 60 - 12 }}}
(2) {{{ 12t = 48 }}}
(2) {{{ t = 4 }}}
OK