Question 590923
Let {{{ s }}} = the speed of the boat
Let {{{ c }}} = the speed of the current
{{{ s + c }}} = the speed going downstream
{{{ s - c }}} = the speed going upstream
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Going downstream:
{{{ s + c = 15/3 }}}
{{{ s + c = 5 }}} mi/hr
Going upstream:
{{{ s - c = 15/5 }}}
{{{ s - c = 3 }}} mi/hr
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Add these equations:
{{{ s + c = 5 }}}
{{{ s - c = 3 }}}
{{{ 2s = 8 }}}
{{{ s = 4 }}}
The speed of the boat is 4 mi/hr
check answer:
{{{ s + c = 5 }}}
{{{ 4 + c = 5 }}}
{{{ c = 1 }}} mi/hr
Going downstream:
r*t = d
{{{ ( 4 + 1)*3 = 15 }}}
Going upstream:
{{{ ( 4 - 1)*5 = 15 }}}
OK