Question 1086593
Let {{{ t }}} = time in hrs to complete the 
swimming part of the race
{{{ 6.5 - t }}} = time in hrs to complete the
running part
Let {{{ d }}} = distance in km that he swam
{{{ 73.5 - d }}} = distance in km that he ran
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Equation for the swimming part:
(1) {{{ d = 3t }}}
Equation for the running part:
(2) {{{ 73.5 - d = 15*( 6.5 - t ) }}}
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Plug (1) into (2)
(2) {{{ 73.5 - 3t = 15*( 6.5 - t ) }}}
(2) {{{ 73.5 - 3t = 97.5 - 15t }}}
(2) {{{ 12t = 24 }}}
(2) {{{ t = 2 }}}
and
{{{ 6.5 - t = 6.5 - 2 }}}
{{{ 6.5 - t = 4.5 }}}
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He took 2 hrs to finish the swimming part
He took 4.5 hrs to finish the running part
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check:
(1) {{{ d = 3t }}}
(1) {{{ d = 3*2 }}}
(1) {{{ d = 6 }}} km
and
(2) {{{ 73.5 - d = 15*( 6.5 - t ) }}}
(2) {{{ 73.5 - d = 15*( 6.5 - 2 ) }}}
(2) {{{ 73.5 - d = 15*4.5 }}}
(2) {{{ 73.5 - d = 67.5 }}}
(2) {{{ d = 6 }}}
OK