Question 715782
Let {{{ c }}} = the speed of the current in km/hr
Let {{{ b }}} = the speed of the boat in still water in km/hr
{{{ b - c }}} = the speed going upstream in km/hr
{{{ b + c }}} = the speed going downstream in km/hr
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Going upstream:
(1) {{{ 36 = ( b - c )*3 }}}
Going downstream:
(2) {{{ 36 = ( b + c )*2 }}}
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(1) {{{ b - c = 12 }}}
(2) {{{ b + c = 18 }}}
Add the equations
{{{ 2b = 30 }}}
{{{ b = 15 }}}
Plug this result back into (1) or (2)
(2) {{{ 15 + c = 18 }}}
(2) {{{ c = 3 }}}
The speed of the boat in still water was 15 mk/hr
The speed of the current was 3 km/hr