Question 1070756
Convert 135 min to hrs:
{{{ 135*( 1/60 ) = 2.25 }}} 
Let {{{ d }}} = the one-way distance up the hill
Let {{{ s }}} = his rate coming down the hill
{{{ s - 2.5 }}} = his rate going up the hill
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Going up the hill:
(1) {{{ d = ( s - 2.5 )*6 }}}
Going down the hill:
(2) {{{ d = s*2.25 }}}
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Substitute (2) into (1)
(1) {{{ s*2.25 = ( s - 2.5 )*6 }}}
(1) {{{ 2.25s = 6s - 15 }}}
(1) {{{ 3.75s = 15 }}}
(1) {{{ s = 4 }}}
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His rate coming down the hill is 4 mi/hr
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check:
(2) {{{ d = s*2.25 }}}
(2) {{{ d = 4*2.25 }}}
(2) {{{ d = 9 }}} mi
and
(1) {{{ d = ( s - 2.5 )*6 }}}
(1) {{{ d = ( 4 - 2.5 )*6 }}}
(1) {{{ d = 1.5*6 }}}
(1) {{{ d = 9 }}} mi
OK