Question 383989
boat speed in still water = 15 mph
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let current speed be x mph
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speed upstream = 15-x mph
speed downstream = 15+x mph.

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distance downstream = 12 miles
distance upstream = 9 miles
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time downstream = time upstream
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t = d/t
{{{12/(15+x)=9/(15-x)}}}
cross multiply
12(15-x)=9(15+x)
180-12x=135+9x
-9x   -9x
180-12x-9x=135
-180    -180
-21x=135-180
-21x=-45
/21
x=-45/-21
x= 2.14 mph speed of current
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m.ananth@hotmail.ca