Question 145541
d=r*t
t=d/r
Let x be the rate of the current.
21/(5+x)=9/(5-x)
21(5-x)=9(5+x) Multiply each side by the LCM to eliminate fractions.
105-21x=45+9x
60=30x
x=2 mph
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Check:
21/7=3 hrs
9/3=3 hrs
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Ed