Question 774491
Let {{{ c }}} = the speed of the current
Let {{{ s }}} = their speed paddling in still water
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Equation for going downstream:
(1) {{{ 20 = ( s + c )*4 }}}
Equation for going upstream:
(2) {{{ 20 = ( s - c )*6 }}}
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(1) {{{ 4s + 4c = 20 }}}
(1) {{{ s + c = 5 }}}
and
(2) {{{ 6s - 6c = 20 }}}
(2) {{{ 3s - 3c = 10 }}}
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Multiply both sides of (1) by {{{ 3 }}}
and add the equations
(2) {{{ 3s - 3c = 10 }}}
(1) {{{ 3s + 3c = 15 }}}
{{{ 6s = 25 }}}
{{{ s = 4.167 }}} mi/hr
and
(1) {{{ s + c = 5 }}}
(1) {{{ 4.167 + c = 5 }}}
(1) {{{ c = .833 }}} mi/hr
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check:
(1) {{{ 20 = ( s + c )*4 }}}
(1) {{{ 20 = ( 4.167 + .833 )*4 }}}
(1) {{{ 20 = 5*4 }}}
(1) {{{ 20 = 20 }}}
and
(2) {{{ 20 = ( s - c )*6 }}}
(2) {{{ 20 = ( 4.167 - .833 )*6 }}}
(2) {{{ 20 = 3.333*6 }}}
(2) {{{ 20 = 20 }}}
OK