Question 901434
A crew times itself on a three-mile course. The three miles upstream takes 20 minutes, and the three miles downstream takes 12 minutes. Find the rate of the crew in still water.
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let x=rate in still water
let c=rate of current
x+c=rate of crew downstream
x-c=rate of crew upstream
distance/speed=travel time
..
12 min=1/5 hr
20 min=1/3 hr
{{{3/(x+c)=1/5}}}
{{{3/(x-c)=1/3}}}
x+c=15
x-c=9
add
2x=24
x=12
c=x-9
c=3
rate in still water=12 mph