Question 599470
Let {{{ c }}} = the speed in mi/hr of the current
Let {{{ s }}} = the speed in mi/hr of the boat in still water
Let {{{ d }}} = distance traveled in mi
Let {{{ t }}} = time in hours
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Going downriver:
{{{ d = ( s + c )*t }}}
(1) {{{ 63 = ( 18 + c )*t }}}
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Going upriver:
{{{ d = ( s - c)*t }}}
(2) {{{ 45 = ( 18 - c )*t }}}
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(1) {{{ t = 63/( 18 + c ) }}}
(2) {{{ t = 45/( 18 - c ) }}}
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{{{ 63/( 18 + c ) = 45/( 18 - c ) }}}
{{{ 63*( 18 - c ) = 45*( 18 + c ) }}}
{{{ 1134 - 63c = 810 + 45c }}}
{{{ 108c = 324 }}}
{{{ c = 3 }}}
The speed of the current is 3 mi/hr
check:
(1) {{{ t = 63/( 18 + 3 ) }}}
(2) {{{ t = 45/( 18 - 3 ) }}}
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(1) {{{ t = 63/21 }}}
(1) {{{ t = 3 }}} hrs
(2) {{{ t = 45/15 }}}
(2) {{{ t = 3 }}} hrs
OK