Question 373485
Let {{{b}}} = the speed of the boat with no current
Let {{{c}}} = the speed of the current
{{{b - c}}} = speed of boat going against current
{{{b + c}}} = speed of boat going with the current
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given:
{{{b - c = 2/5.5}}}
{{{b + c = 9/5.5}}}
Now you can just add these equations
{{{2b = 2/5.5 + 9/5.5}}}
{{{2b = 11/5.5}}}
{{{b = 11/11}}}
{{{b = 1}}}
and, since
{{{b + c = 9/5.5}}}
{{{c = 9/5.5 - 1}}}
{{{c = 18/11 - 11/11}}}
{{{c = 7/11}}}
The boat in still water goes 1 mi/hr
The speed of the current is 7/11 mi/hr
check answer:
{{{b - c = 2/5.5}}}
{{{11/11 - 7/11 = 4/11}}}
{{{4/11 = 4/11}}}
and
{{{b + c = 9/5.5}}}
{{{11/11 + 7/11 = 18/11}}}
{{{18/11 = 18/11}}}
OK