Question 938021
Going upstream, his speed is {{{ 15 }}} km/hr
Going downstream, his speed is {{{ 15/3 = 5 }}} km/hr
Let {{{ s }}} = his speed rowing in still water
Let {{{ c }}} = the speed of the current
{{{ s - c }}} = his speed rowing upstream
{{{ s + c }}} = his speed rowing downstream
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I can say:
{{{ ( s + c ) - ( s - c ) = 15 - 5 }}}
{{{ s + c - s + c = 10 }}}
{{{ 2c = 10 }}}
{{{ c = 5 }}} km/hr
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Plug this back in:
{{{ s + c = 15 }}}
{{{ s + 5 = 15 }}}
{{{ s = 10 }}} km/hr
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In still water:
{{{ d = 10*3 }}}
{{{ d = 30 }}}
He can row 30 km in 3 hrs in still water
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check:
{{{ s - c = 5 }}}
{{{ 10 - 5 = 5 }}}
{{{ 5 = 5 }}}
OK