Question 263749
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How far upstream can a motorboat travel at 8 mi/hr and still return downstream at 12 mi/hr in a total time of 4 hr?
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        The solution in the post by @mananth is INCORRECT due to arithmetic error.

        His answer "3 hours upstream and 1 hour downstream" does not work, as everybody can check manually.

        I came to bring a correct solution.



let the time taken upstream be x
the down stream time will be 4-x hrs.
speed upstream = 8 mph
distance upstream = 8*x
distance downstream = 12*(4-x)
8x = 48-12x
20x = 48
x = 48/20 = 2.4 hours = 2 hours and 24 minutes ---------------------------------- 24 miles
downstream time = 4 hours - 2.4 hours = 1.6 hours = 1 hour and 36 minutes.


The one way distance is  2.4 hours upstream * 8 mph = 19.2 miles.


<U>ANSWER</U>.  How far is 19.2 miles.


Solved correctly.