Question 766469
Let {{{ x }}} = rate of rowing in still water in mi/hr
Let {{{ y }}} = rate of the current in mi/hr
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Rowing with the current:
(1) {{{ 18 = ( x + y )*2 }}}
Rowing against the current:
(2) {{{ (5/9)*18 = ( x - y )*2 }}}
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(2) {{{ 10 = 2x - 2y }}}
and
(1) {{{ 18 = 2x + 2y }}}
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Add the equations:
{{{ 28 = 4x }}}
{{{ x = 7 }}}
Plug this result into (1) or (2)
(2) {{{ 10 = 2x - 2y }}}
(2) {{{ 5 = x - y }}}
(2) {{{ 5 = 7 - y }}}
(2) {{{ y = 7 - 5 }}}
(2) {{{ y = 2 }}}
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The rate of rowing in still water is 7 mi/hr
The rate of the current is 2 mi/hr
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check:
(2) {{{ (5/9)*18 = ( 7 - 2 )*2 }}} 
(2) {{{ 10 = 5*2 }}}
(2) {{{ 10 = 10 }}}
and
(1) {{{ 18 = ( 7 + 2 )*2 }}}
(1) {{{ 18 = 9*2 }}}
(1) {{{ 18 = 18 }}}
OK