Question 1040900
let {{{ d[1] }}} = Ethan's head start in miles
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Start a stopwatch when Seth leaves and let
{{{ t }}}  = time in hours on stopwatch when 
Seth catches up with Ethan
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Ethan's equation:
(1) {{{ 60 - d[1] = 10t }}}
Seth's equation:
(2) {{{ 60 = 15t }}}
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(2) {{{ t = 60/15 }}}
(2) {{{ t = 4 }}} 
Substitute this result into (1)
(1) {{{ 60 - d[1] = 10*4 }}}
(1) {{{ d[1] = 60 - 40 }}}
(1) {{{ d[1] = 20 }}}
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Let {{{ t[1] = Ethan's head start in hours
{{{ d[1] = 10*t[1] }}}
{{{ 20 = 10t[1] }}}
{{{ t[1] = 2 }}}
Ethan's head start was 120 minutes
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check:
(2) {{{ 60 = 15t }}}
(2) {{{ 60 = 15*4 }}}
(2) {{{ 60 = 60 }}}
OK
(1) {{{ 60 - d[1] = 10t }}}
(1) {{{ 60 - 20 = 10*4 }}}
(1) {{{ 40 = 40 }}}
OK
feel free to get 2nd opinion