SOLUTION: A boat travels 100 miles downstream in the same length of time it travels 50 miles upstream. if the boat's speed in still water is 30 mph, find the speed of the current river.

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Question 138852: A boat travels 100 miles downstream in the same length of time it travels 50 miles upstream. if the boat's speed in still water is 30 mph, find the speed of the current river.
Answer by ankor@dixie-net.com(22740) (Show Source):
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A boat travels 100 miles downstream in the same length of time it travels 50 miles upstream. if the boat's speed in still water is 30 mph, find the speed of the current river.
:
Let x = speed of the current:
:
(30-x) = speed upstream
(30+x) = speed down stream
;
the times of the two trips are given as equal:
write a time equation: Time = dist/speed
;
=
Cross multiply:
50(30+x) = 100(30-x)
:
1500 + 50x = 3000 - 100x
:
50x + 100x = 3000 - 1500
:
150x = 1500
x =
x = 10 mph is the speed of the current:
:
:
Check solution by finding the times of each trip:
100/40 = 2.5 hrs
50/20 = 2.5 hrs