Question 1128948
Let the rate of the current = {{{ c }}}
Swimmer's rate swimming with the current:
{{{ 4 + c }}}
Swimmer's rate swimming against the current:
{{{ 4 - c }}}
Let {{{ t }}} = time in hrs for both trips
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Swimming with the current:
(1) {{{ 27 = ( 4 + c )*t }}}
Swimming against the current
(2) {{{ 9 = ( 4 - c )*t }}}
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(1) {{{ t = 27/( 4 + c ) }}}
(2) {{{ t = 9/( 4 - c ) }}}
{{{ 27/( 4 + c ) = 9/( 4 - c ) }}}
{{{ 27*( 4 - c ) = 9*( 4 + c ) }}}
{{{ 3*( 4 - c ) = 4 + c }}}
{{{ 12 - 3c = 4 + c }}}
{{{ 4c = 8 }}}
{{{ c = 2 }}}
The speed of the current is 2 mi/hr
check:
(1) {{{ t = 27/( 4 + 2 ) }}}
(1) {{{ t = 9/2 }}}
and
{{{ t = 9/( 4 - 2 ) }}}
{{{ t = 9/2 }}}
OK