Question 882368
Let {{{ s }}} = the speed of the boat in still water
Let {{{ c }}} = the speed of the current
{{{ s + c }}} = the speed of the boat going downstream
{{{ s - c }}} = the speed of the boat going upstream
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(1) {{{ 78 = ( s + c )*3.25 }}}
(2) {{{ 72 = ( s - c )*7.2 }}}
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(1) {{{ s + c = 24 }}}
(2) {{{ s - c = 10 }}}
Add the equations
{{{ 2s = 34 }}}
{{{ s = 17 }}}
and, since
(2) {{{ s - c = 10 }}}
(2) {{{ c = s - 10 }}}
(2) {{{ c = 17 - 10 }}}
(2) {{{ c = 7 }}}
The speed of the boat in still water is 17 mi/hr
The speed of the current is 7 mi/hr
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check:
(1) {{{ 78 = ( s + c )*3.25 }}}
(1) {{{ 78 = ( 17 + 7 )*3.25 }}}
(1) {{{ 78 = 24*3.25 }}}
(1) {{{ 78 = 78 }}}
You can check other equation