Question 365519
A motorboat has a four-hour supply of gasoline.
 How far from the marina can it travel if the rate going out against the
 current is 20 mi/h and the rate coming back with the current is 30 mi/h?
:
Let d = the one-way distance (dist from marina)
Write a time equation: time = dist/speed
:
out time + return time = 4 hrs
{{{d/20}}} + {{{d/30}}} = 4
multiply by 60, to clear the denominators, results:
3d + 2d = 60(4)
5d = 240
d = {{{240/5}}}
d = 48 miles
:
:
see if that's true, find the time each way
48/20 = 2.4 hrs
48/30 = 1.6 hrs
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totals: 4.0 hrs; confirms our solution of 48 mi