Question 83625
s = rate of stream
b = rate of boat
For downstream:
{{{d = (b + s)*t}}}
For upstream:
{{{d = (b - s)*t}}}
{{{84 = (b + s)*2}}}
{{{84 = 2b + 2s}}}
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{{{84 = (b - s)*6}}}
{{{84 = 6b - 6s}}}
Multiply the 1st equation by 3
and add to the second
{{{252 = 6b + 6s}}}
{{{84 = 6b - 6s}}}
{{{336 = 12b}}}
{{{b = 28}}} This is the speed of the boat in still water in mph
{{{84 = 2b + 2s}}}
{{{84 = 2*28 + 2s}}}
{{{2s = 84 - 56}}}
{{{2s = 28}}}
{{{s = 14}}}Rate of stream in mph