Question 1027283
Let {{{ t }}} = time in hours for the car
{{{ 20 - t }}} = time in hours for the train
Let {{{ s }}} = the speed of the car in km/hr
{{{ 2s }}} = the speed of the train in km/hr
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Equation for the car:
(1) {{{ 400 = s*t }}}
Equation for the train:
(2) {{{ 2000 = 2s*( 20 - t ) }}}
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(1) {{{ s = 400/t }}}
Substitute (1) into (2)
(2) {{{ 2000 = 2*( 400/t )*( 20 - t ) }}}
(2) {{{ 2000 = 2*( 8000/t - 400 ) }}}
(2) {{{ 2000 = 16000/t - 800 }}}
(2) {{{ 20 = 160/t - 8 }}}
(2) {{{ 160/t = 28 }}}
(2) {{{ t = 160/28 }}}
(2) {{{ t = 40/7 }}}
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(1) {{{ 400 = s*t }}}
(1) {{{ 400 = s*( 40/7 ) }}} 
(1) {{{ 2800 = 40s }}}
(1) {{{ s = 70 }}}
and
{{{ 2s = 2*70 }}}
{{{ 2s = 140 }}}
the speed of the train is 140 km/hr
(2) {{{ 2000 = 2s*( 20 - t ) }}}
(2) {{{ 2000 =140*( 20 - t ) }}}
(2) {{{ 100/7 = 20 - t }}}
(2) {{{ t = 20 - 100/7 }}}
(2) {{{ t = 140/7 - 100/7 }}}
(2) {{{ t = 40/7 }}}
OK